
<PAGE>
                                                                   Exhibit 2.4


                                       FORM OF
                                CERTIFICATE OF MERGER
                                       MERGING 
                           WHISTLER ACQUISITION CORPORATION
                                    WITH AND INTO
                                  HEARTSTREAM, INC.

                                     ___________

              Pursuant to Section 251 of the General Corporation Law of 
                                the State of Delaware
                                     ___________



     Heartstream, Inc., a Delaware corporation ("Heartstream"), DOES HEREBY
CERTIFY AS FOLLOWS:

     FIRST:  That Heartstream was incorporated on December 3, 1992 pursuant to
the Delaware General Corporation Law (the "Delaware Law").  Whistler Acquisition
Corporation ("Merger Sub") was incorporated on December 24, 1997 pursuant to the
Delaware Law.

     SECOND:  That an Agreement and Plan of Reorganization (the "Reorganization
Agreement"), dated as of December 29, 1997, among Hewlett-Packard Company, a
California corporation, Merger Sub and Heartstream, setting forth the terms and
conditions of the merger of Merger Sub with and into Heartstream (the "Merger"),
has been approved, adopted, certified, executed and acknowledged by each of the
constituent corporations in accordance with the requirements of Section 251 of
the Delaware Law.

     THIRD:  That the name of the surviving corporation (the "Surviving
Corporation") shall be Heartstream, Inc.

     FOURTH:  From and after the effective time of the Merger, the Certificate
of Incorporation of Merger Sub shall continue to be the Certificate of
Incorporation of the Surviving Corporation, until amended as provided by the
law.

     FIFTH:  That an executed copy of the Reorganization Agreement is on file at
the principal place of business of the Surviving Corporation at the following
address:

                         Heartstream, Inc.
                         2401 Fourth Avenue, Suite 300
                         Seattle, Washington 98121

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     SIXTH:  That a copy of the Reorganization Agreement will be furnished by
the Surviving Corporation, on request and without cost, to any stockholder of
any constituent corporation.

     SEVENTH:  That the Merger shall become effective upon the filing of this
Certificate of Merger with the Secretary of State of the State of Delaware.

     IN WITNESS WHEREOF, Heartstream has caused this Certificate of Merger to be
executed in its corporate name as of the ____ day of _____ 1998.

                         Heartstream, Inc. 
                         By:
                             -------------------
                             Alan Levy

