X0306 4 2020-05-04 0 0001552451 MyoKardia, Inc. MYOK 0001413822 GIANAKAKOS ANASTASIOS C/O MYOKARDIA, INC. 1000 SIERRA POINT PARKWAY BRISBANE CA 94005 1 1 0 0 President and CEO Common Stock 2020-05-04 4 S 0 1386 56.9317 D 77736 D Common Stock 2020-05-04 4 S 0 400 58.045 D 77336 D Common Stock 2020-05-04 4 S 0 2909 59.0979 D 74427 D Common Stock 2020-05-04 4 S 0 305 60.152 D 74122 D Common Stock 130407 I By Reporting Person's Trust 2 Common Stock 300000 I By Reporting Person's Trust 4 Common Stock 6000 I By Reporting Person's Trust 5 Common Stock 53087 I By Trust 1 Common Stock 53087 I By Trust 2 Common Stock 53087 I By Trust 3 This transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person. Represents the weighted average sale price of the shares sold ranging from $56.46 to $57.35 per share. The Reporting Person will provide, upon request by the Commission staff, the Issuer, or a security holder of the Issuer, full information regarding the number of shares sold at each separate price within the ranges reported in footnotes 2, 4, 5 and 6. Includes 95,540 shares previously held by The TKG Trust dated November 2, 2006 which were contributed to the Reporting Person directly on May 1, 2020, and excludes (a) 300,000 shares previously owned directly which were contributed to The Tassos Gianakakos 2020 Annuity Trust on May 1, 2020 and (b) 6,000 shares previously owned directly which were contributed to The TKG 2020 Irrevocable Trust on May 1, 2020. Represents the weighted average price of the shares sold ranging from $57.48 to $58.40 per share. Represents the weighted average price of the shares sold ranging from $58.60 to $59.45 per share. Represents the weighted average price of the shares sold ranging from $59.67 to $60.17 per share. Excludes 95,540 shares previously held by The TKG Trust dated November 2, 2006 which were contributed to the Reporting Person directly on May 1, 2020. Includes 300,000 shares previously owned directly which were contributed to The Tassos Gianakakos 2020 Annuity Trust on May 1, 2020. Includes 6,000 shares previously owned directly which were contributed to The TKG 2020 Irrevocable Trust on May 1, 2020. /s/ Cynthia J. Ladd, as Attorney-in-Fact 2020-05-06