SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                               -----------------

                                  SCHEDULE 13G

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                              (Amendment No.) /1/

                                 CryoCor, Inc.
                                (Name of Issuer)

                    Common Stock, par value $0.001 per share
                         (Title of Class of Securities)

                                   229016100
                                 (CUSIP Number)

                               December 31, 2006
            (Date of Event Which Requires Filing of This Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

      |_|   Rule 13d-1(b)
      |_|   Rule 13d-1(c)
      |X|   Rule 13d-1(d)

-----------
      /1/ The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which would
alter disclosures provided in a prior cover page.

      The information required in the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).



CUSIP No. 229016100                   13G                     Page 2 of 11 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Partners VII QP, L.P.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          1,848,408 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            1,848,408 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     1,848,408 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     17.11%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------



CUSIP No. 229016100                   13G                     Page 3 of 11 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Partners VII, L.P.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          1,848,408 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            1,848,408 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     1,848,408 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     17.11%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     OO
--------------------------------------------------------------------------------



CUSIP No. 229016100                   13G                     Page 4 of 11 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Management VII, L.C.C.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          1,848,408 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            1,848,408 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     1,848,408 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     17.11%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------



CUSIP No. 229016100                   13G                     Page 5 of 11 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Management VII, L.P.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          1,848,408 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            1,848,408 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     1,848,408 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     17.11%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------



                                  SCHEDULE 13G

Item 1(a).  Name of Issuer:

            CryCor, Inc. (the "Company")

Item 1(b).  Address of Issuer's Principal Executive Offices:

            9717 Pacific Heights Blvd.
            San Diego, CA 92121

Item 2(a).  Name of Persons Filing:

            This statement is filed jointly by each of the following Persons
            pursuant to Rule 13d-1(k) promulgated by the Securities and Exchange
            Commission ("SEC") under Section 13 of the Securities Exchange Act
            of 1934, as amended (the "Act"): (i) William Blair Capital Partners
            VII QP, L.P., a Delaware limited partnership (the "Fund"), by virtue
            of its direct beneficial ownership of Common Stock and (ii) William
            Blair Capital Partners VII, L.P., a Delaware limited partnership
            (the "Fund"), by virtue of its direct beneficial ownership of Common
            Stock and (iii) William Blair Capital Management VII, L.L.C.
            ("WBCPCO," together with the Fund, each a "Reporting Person" and
            collectively, "Reporting Persons"), a Delaware limited liability
            company, by virtue of its being the general partner of the general
            partner of the Fund. (iv) William Blair Capital Management VII, L.P.
            ("WBCPCO," together with the Fund, each a "Reporting Person" and
            collectively, "Reporting Persons"), a Delaware limited liability
            company, by virtue of its being the general partner of the Fund. By
            virtue of being members of the Board of Managers of WBCPCO (the
            "Board"), Timothy Burke, John Ettelson, Robert D. Blank, David G.
            Chandler, Arda Minocherhomjee, Timothy M. Murray, and Robert Healy
            may be deemed to possess indirect beneficial ownership of the Common
            Stock, but such beneficial ownership is disclaimed. Only the Board,
            acting upon the consent of a majority of the members of the Board at
            any meeting of the Board where a quorum is present, possesses the
            right to vote, direct the vote, dispose or direct the disposition of
            the Common Stock. No individual has sole power to vote, direct the
            vote, dispose or direct the disposition of the Common Stock. The
            Reporting Persons have entered into an Agreement Related to the
            Joint Filing of Schedule 13G, dated February 9, 2007, a copy of
            which is filed with this Schedule 13G as Exhibit A, pursuant to
            which the Reporting Persons have agreed to file this statement
            jointly in accordance with the provisions of Rule 13d-1(k) under the
            Act. Information with respect to each of the Reporting Persons is
            given solely by such Reporting Person, and no Reporting Person
            assumes responsibility for the accuracy or completeness of
            information provided by another Reporting Person. By their signature
            on this statement, each of the Reporting Persons agrees that this
            statement is filed on behalf of such Reporting Person. The Reporting
            Persons may be deemed to constitute a "group" for purposes of
            Section 13(d)(3) of the Act. The Reporting Persons expressly
            disclaim that they have agreed to act as a group other than as
            described in this statement.

Item 2(b).  Address of Principal Business Office or, if none, Residence:

            The address of the principal business office of each of the
            Reporting Persons is 222 West Adams Street, Chicago, Illinois 60606.

Item 2(c).  Citizenship:

            The Fund is a Delaware limited partnership and WBCPCO is a Delaware
            limited liability company.


                                  Page 6 of 11


Item 2(d).  Title of Class of Securities:

            Common Stock, par value $0.001 per share ("Common Stock").

Item 2(e).  CUSIP No.:

            229016100

Item 3.     If this statement is filed pursuant to Rules 13d-1(b) or 13d-2(b) or
            (c), check whether the person filing is a:

            Not Applicable.

Item 4.     Ownership (as of December 31, 2006):

            As of December 31, 2006, the Fund was the registered owner Of
            1,848,408 shares of Common Stock or approximately 17.11% of the
            total number of shares of Common Stock outstanding as of such date
            (based upon information provided by the Company). By virtue of the
            relationship between the Fund and WBCPCO described in Item 2(a),
            WBCPCO may be deemed to possess indirect beneficial ownership of and
            shares the power to vote or direct the vote of the shares of Common
            Stock beneficially owned by the Fund. WBCPCO disclaims beneficial
            ownership of the shares of Common Stock owned by the Fund. The
            filing of this statement by WBCPCO shall not be construed as an
            admission that they are, for the purpose of Section 13(d) or Section
            13(g) of the Act, the beneficial owner of any securities covered by
            this statement.

Item 5.     Ownership of Five Percent or Less of a Class:

            Not Applicable.

Item 6.     Ownership of More Than Five Percent on Behalf of Another Person:

            Not Applicable.

Item 7.     Identification and Classification of the Subsidiary Which Acquired
            the Security Being Reported on By the Parent Holding Company:

            Not Applicable.

Item 8.     Identification and Classification of Members of the Group:

            Not Applicable.

Item 9.     Notice of Dissolution of a Group:

            Not Applicable.

Item 10.    Certification:

            Not Applicable.


                                  Page 7 of 11


                                    SIGNATURE

      After reasonable inquiry and to the best of our knowledge and belief, the
undersigned certify that the information set forth in this statement is true,
complete and correct.

Date: February 9, 2007

                               WILLIAM BLAIR CAPITAL PARTNERS VII QP, L.P.

                               By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                               By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                    --------------------------------------------
                                    Title: Managing Director


                               William Blair Capital Management VII, L.P.

                               By:  William Blair Capital Management VII, L.L.C.
                               Its:  General Partner

                               By: /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                               William Blair Capital Management VII, L.L.C.

                               By: /s/ David G. Chandler
                               -----------------------------------------------
                               Title: Managing Director


                                  Page 8 of 11


                               WILLIAM BLAIR CAPITAL PARTNERS VII, L.P.

                               By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                               By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                    --------------------------------------------
                                    Title: Managing Director


                               William Blair Capital Management VII, L.P.

                               By:  William Blair Capital Management VII, L.L.C.
                               Its:  General Partner

                               By: /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                               William Blair Capital Management VII, L.L.C.

                               By:  /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                                  Page 9 of 11


EXHIBIT A

                     AGREEMENT REGARDING THE JOINT FILING OF
                                  SCHEDULE 13G

                             -----------------------

William Blair Capital Partners VII QP, L.P., William Blair Capital Partners VII,
L.P., William Blair Capital Management VII, L.L.C. and William Blair Capital
Management VII, L.P. hereby agree that the Statement on Schedule 13G to which
this agreement is attached as an exhibit, as well as all future amendments to
such Statement, shall be filed jointly on behalf of each of them. This agreement
is intended to satisfy the requirements of Rule 13d-1(k) (1) (iii) under the
Securities Exchange Act of 1934, as amended.

Date: February 9, 2007

                               WILLIAM BLAIR CAPITAL PARTNERS VII QP, L.P.

                               By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                               By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                    --------------------------------------------
                                    Title: Managing Director


                               William Blair Capital Management VII, L.P.

                               By: William Blair Capital Management VII, L.L.C.
                               Its: General Partner

                               By: /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                               William Blair Capital Management VII, L.L.C.

                               By:  /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                                 Page 10 of 11


                               WILLIAM BLAIR CAPITAL PARTNERS VII, L.P.

                               By:  William Blair Capital Management VII, L.P.
                                     Its: General Partner

                               By:  William Blair Capital Management VII, L.L.C.
                                     Its: General Partner

                                     By: /s/ David G. Chandler
                                     -------------------------------------------
                                     Title: Managing Director


                               William Blair Capital Management VII, L.P.

                               By:  William Blair Capital Management VII, L.L.C.
                               Its:  General Partner

                               By: /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                               William Blair Capital Management VII, L.L.C.

                               By:  /s/ David G. Chandler
                               -------------------------------------------------
                               Title: Managing Director


                                 Page 11 of 11