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                                                                    EXHIBIT 10.4

                         HORIZON MEDICAL PRODUCTS, INC.
                     AMENDMENT NO. 1 TO AMENDED AND RESTATED
                            SECURITYHOLDERS AGREEMENT

This Amendment No. 1 to Amended and Restated Securityholders Agreement (this
"Amendment") is entered into as of May 12, 2004, by and among Horizon Medical
Products, Inc., a Georgia corporation (the "Company"), ComVest Venture Partners,
L.P., a Delaware limited partnership ("ComVest"), Medtronic, Inc., a Minnesota
corporation ("Medtronic" and, together with ComVest, each, an "Investor," and,
together, the "Investors"), and Marshall Hunt (a "Major Stockholder" and,
together with the Investors, the "Company Stockholders").

                                   BACKGROUND

      A. The Company, the Company Stockholders and Standard Federal Bank
National Association, a national banking association, acting by and through
LaSalle Business Credit, Inc., a Delaware corporation, are parties to that
certain Amended and Restated Securityholders Agreement, dated as of October 21,
2003 (the "Agreement"). Capitalized terms used herein without definition shall
have the meanings ascribed to them in the Agreement.

      B. The Company, RITA Medical Systems, Inc., a Delaware corporation
("Parent"), and Hornet Acquisition Corp., a Delaware corporation and
wholly-owned subsidiary of Parent ("Merger Sub"), have entered into an Agreement
and Plan of Merger, dated as of May __, 2004 (the "Merger Agreement"), which
provides for the merger of Merger Sub with and into the Company (the "Merger"),
pursuant to which the Company shall become a wholly-owned subsidiary of Parent.

      C. Pursuant to Section 6.6 of the Agreement, the Agreement may be amended
in any manner with the written consent of the record or beneficial holders of at
least eighty percent (80%) of the Registrable Securities held by the Holders and
the Company, when authorized by resolution of its Board of Directors.

      D. The termination of the Agreement as of the Effective Time is a
condition to the obligation of Parent and Merger Sub to consummate the
transactions contemplated by the Merger Agreement.

      E. As a condition and inducement to the willingness of Parent and Merger
Sub to consummate the transactions contemplated by the Merger Agreement, the
parties hereto desire to amend the Agreement as set forth herein.

                                    AMENDMENT

      1. Termination. The following Section 6.14 is hereby added to the
Agreement:

            "6.14 Notwithstanding anything in the this Agreement to the
      contrary, this Agreement shall terminate and be of no further force and
      effect immediately before the Effective Time of the Merger, pursuant the
      Merger. For purposes of this Agreement, "Effective Time" shall have the
      meaning ascribed to it in the Merger Agreement."

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      2. Consent. Notwithstanding any provision in the Agreement to the
contrary, including, without limitation, Sections 3 and 5.6, ComVest and
Medtronic hereby consent to the Major Stockholder's entering into the agreements
and the transactions contemplated by the Merger Agreement, including, without
limitation, the Voting Agreement and the Lock Up Agreement (as such terms are
defined in the Merger Agreement). ComVest and Medtronic hereby waive any
provision of the Agreement which may be in conflict with any action taken or
agreement signed by the Major Stockholder in connection with the Merger, and
ComVest and Medtronic acknowledge that no such action or agreement will
constitute an Event of Default under the Agreement.

      3. Miscellaneous.

            3.1 Full Force and Effect. Except as expressly amended hereby, the
Agreement shall continue in full force and effect in accordance with the
provisions thereof on the date hereof.

            3.2 Counterparts. This Amendment may be signed in one or more
counterparts, all of which shall be considered one and the same instrument.

                            [signature page follows]

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      IN WITNESS WHEREOF, the Company and the Company Stockholders have caused
this Amendment to be duly executed as of the day and year first above written.

HORIZON MEDICAL PRODUCTS, INC.



By: /s/ Robert J. Wenzel
    ----------------------------------

Name: Robert J. Wenzel
      --------------------------------

Title: Interim CEO
       -------------------------------

COMVEST VENTURE PARTNERS, L.P.


By: /s/ Harold Blue
    ----------------------------------
Name: Harold Blue
      --------------------------------
Title: Partner/President
       -------------------------------
MEDTRONIC, INC.


By: /s/ Michael D. Ellwein
       -------------------------------
Name: Michael D. Ellwein
       -------------------------------
Title: Vice President and Chief
       Development Officer
       -------------------------------

MAJOR STOCKHOLDER

/s/ Marshall Hunt
--------------------------------------
Marshall Hunt

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO
                            SECURITYHOLDERS AGREEMENT

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