X0306 4/A 2020-06-29 2020-07-01 0 0001552451 MyoKardia, Inc. MYOK 0001104268 CRANSTON MARY B C/O MYOKARDIA, INC. 1000 SIERRA POINT PARKWAY BRISBANE CA 94005 1 0 0 0 Common Stock 2020-06-29 4 M 0 371 11.69 A 2671 D Common Stock 2020-06-29 4 S 0 371 98.6821 D 2300 D Common Stock 2020-06-30 4 M 0 21629 11.69 A 23929 D Common Stock 2020-06-30 4 S 0 300 97.2547 D 23629 D Common Stock 2020-06-30 4 S 0 21329 96.5905 D 2300 D Represents the weighted average sale price of the shares sold ranging from $98.50 to $98.725 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 for all transactions within the ranges set forth in footnotes 1 through 3. Represents the weighted average sale price of the shares sold ranging from $97.247 to $97.27 per share. Represents the weighted average sale price of the shares sold ranging from $96.24 to $97.236 per share. This Form 4/A corrects the Reporting Person's balances in Box 5 of Table I. Exhibit List: Exhibit 24.1 - Power of Attorney /s/ Denelle J. Waynick, as Attorney-in-Fact 2020-10-30