X0306 4 2018-06-12 0 0001552451 MyoKardia Inc MYOK 0001385155 Meeker David P C/O MYOKARDIA, INC. 333 ALLERTON AVENUE SOUTH SAN FRANCISCO CA 94080 1 0 0 0 Stock Option (Right to Buy) 48.85 2018-06-12 4 A 0 11000 0.00 A 2028-06-11 Common Stock 11000 11000 D The shares subject to this option shall vest and become exercisable in 12 equal monthly installments with the first installment on July 12, 2018, such that this option is fully exercisable on June 12, 2019. 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). /s/ Jake Bauer, Attorney-in-Fact 2018-06-14