X0508 4 2024-07-02 0000907654 ARCA biopharma, Inc. ABIO 0001274173 JANUS HENDERSON GROUP PLC 201 BISHOPGATE LONDON X0 EC2M 3AE UNITED KINGDOM 1 0002030299 Janus Henderson Biotech Innovation Master Fund Ltd 201 BISHOPGATE LONDON X0 EC2M 3AE UNITED KINGDOM 1 0 Common Stock 2024-07-03 4 P 0 166042 3.5507 A 1648577 I By Fund Common Stock 2024-07-05 4 P 0 23326 3.4303 A 1671903 I By Fund Common Stock 2024-07-05 4 P 0 5000 3.41 A 1676903 I By Fund Common Stock 2024-07-08 4 P 0 29892 3.4114 A 1706795 I By Fund Common Stock 2024-07-08 4 P 0 17600 3.535 A 1724395 I By Fund Common Stock 2024-07-09 4 P 0 16917 3.4339 A 1741312 I By Fund Common Stock 2024-07-10 4 P 0 33500 3.4647 A 1774812 I By Fund Common Stock 2024-07-10 4 P 0 21963 3.4632 A 1796775 I By Fund Common Stock 2024-07-11 4 P 0 94537 3.4516 A 1891312 I By Fund The securities reported are beneficially owned directly by Janus Henderson Biotech Innovation Master Fund Ltd. (the "Fund"). Janus Henderson Group plc has a 100% ownership stake in Janus Henderson Investors US LLC, which serves as the investment advisor to the Fund, and may therefore be deemed a beneficial owner of the securities reported herein. Each Reporting Person disclaims beneficial ownership of the securities reported herein except to the extent of its pecuniary interest therein, if any. /s/ Michelle Rosenberg, CAO, General Counsel & Company Secretary 2024-07-12 /s/ Janus Henderson Biotech Innovation Master Fund Ltd., By: Janus Henderson Investors US LLC, By: Peter Falconer, Assistant Secretary 2024-07-12