X0306 4/A 2020-06-13 2020-06-16 0 0001552451 MyoKardia, Inc. MYOK 0001616640 AGARWAL SUNIL C/O MYOKARDIA, INC. 1000 SIERRA POINT PARKWAY BRISBANE CA 94005 1 0 0 0 Common Stock 2020-06-13 4 M 0 2300 A 2300 D Restricted Stock Units 2020-06-13 4 M 0 2300 0.00 D Common Stock 2300 0 D RSUs convert into common stock on a one-for-one basis. Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock. The shares of Common Stock underlying the RSUs vest in a single installment on the first anniversary of the grant date, such that all of the underlying shares shall be vested on June 13, 2020, subject to the Reporting Person's continued service on the Issuer's Board of Directors. The shares of Common Stock underlying the RSUs are subject to full acceleration of vesting with respect to all then-unvested shares upon the consummation of a Sale Event (as defined in the Issuer's 2015 Stock Option and Incentive Plan, as amended). This Form 4/A corrects the disposition of units in Box 5 of Table II. /s/Cynthia J. Ladd, as Attorney-in-Fact 2020-06-23