X0306 4 2018-02-01 0 0001552451 MyoKardia Inc MYOK 0001217596 LADD CYNTHIA J C/O MYOKARDIA, INC. 333 ALLERTON AVENUE SOUTH SAN FRANCISCO CA 94080 0 1 0 0 General Counsel Stock Option (Right to Buy) 54.05 2018-02-01 4 A 0 120000 0.00 A 2028-01-31 Common Stock 120000 120000 D 1/4th of the underlying shares shall vest on January 16, 2019; thereafter, the shares subject to this option shall vest and become exercisable in 36 equal monthly installments with the first installment on February 16, 2019, such that this option is fully exercisable on January 16, 2022. 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). /s/ Jake Bauer, as Attorney-in-Fact 2018-02-02