X0306 4 2020-06-18 0 0001552451 MyoKardia, Inc. MYOK 0001616640 AGARWAL SUNIL C/O MYOKARDIA, INC. 1000 SIERRA POINT PARKWAY BRISBANE CA 94005 1 0 0 0 Stock Option (Right to Buy) 100.27 2020-06-18 4 A 0 3000 0.00 A 2030-06-17 Common Stock 3000 3000 D Restricted Stock Units 2020-06-18 4 A 0 1800 0.00 A Common Stock 1800 1800 D The shares subject to this option shall vest and become exercisable in 12 equal monthly installments after June 18, 2020, subject to the Reporting Person's continued service on the Issuer's Board of Directors. This option is 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). 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, 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). /s/ Cynthia J. Ladd, as Attorney-in-Fact 2020-06-22