Organization	6 Months Ended
Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization MyoKardia, Inc. (the “Company”) is a clinical-stage biopharmaceutical company pioneering a precision medicine approach to discover, develop and commercialize targeted therapies for the treatment of serious and neglected rare cardiovascular diseases. The Company’s initial focus is on the treatment of heritable cardiomyopathies, a group of rare, genetically driven forms of heart failure that result from biomechanical defects in cardiac muscle contraction. MyoKardia’s most advanced program, mavacamten, is in four clinical trials, including a pivotal Phase 3 study for the treatment of obstructive hypertrophic cardiomyopathy. A second clinical-stage candidate, MYK-491, is in a Phase 2a multiple-ascending dose study in patients with stable systolic heart failure. The Company was incorporated on June 8, 2012 in Delaware and its corporate headquarters and operations are in South San Francisco, California. Liquidity The Company has incurred significant operating losses since inception and has an accumulated deficit of $278.2 million as of June 30, 2019. The Company has relied on its ability to fund its operations through private and public equity financings, and to a lesser extent, through a license and collaboration arrangement with a collaboration partner, Sanofi S.A. (“Sanofi”), via its subsidiary, Aventis Inc. As discussed further in Note 3, the collaboration agreement with Sanofi ended on December 31, 2018 and the Company no longer records revenues from Sanofi nor has it received reimbursements of research and development expenses after June 30, 2019. The Company has not yet received regulatory approval to commercialize or sell any product and does not have customers. Management expects operating losses and negative operating cash flows to continue for the foreseeable future. As the Company continues to incur losses, a transition to profitability is dependent upon the successful development, approval, and commercialization of the Company’s products and product candidates and the achievement of a level of revenues adequate to support its cost structure. The Company’s ultimate success depends on the outcome of its research and development activities. The Company anticipates the need to raise additional capital to fully implement its business plan and intends to raise such capital through the issuance of additional equity, debt and/or strategic alliances with partner companies. There is no assurance that such financing will be available on terms acceptable to the Company, if at all. On March 8, 2018, the Company filed a Registration Statement on Form S-3ASR (the “2018 Shelf Registration Statement”) covering the potential offering, issuance, and sale of an indeterminate amount of common stock, preferred stock, debt securities, warrants and/or units. In March 2019, the Company completed a follow-on offering under the 2018 Shelf Registration Statement in which the Company issued 5,663,750 shares of common stock at a price of $51.00 per share, including 738,750 shares sold directly to the underwriters upon exercise of their option to purchase up to 738,750 shares of the Company’s common stock within 30 days of the offering. During the six months ended June 30, 2019, the Company received proceeds totaling approximately $271.2 million from the offering, net of underwriting discounts and commissions and offering expenses. As of June 30, 2019, the Company had $602.4 million of cash, cash equivalents and investments (short-term and long-term) and management believes that these amounts will be sufficient to meet the Company’s anticipated operating and capital expenditure requirements for the twelve months following the issuance date of this Form 10-Q. Management’s belief with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional funding.

Organization

6 Months Ended

Jun. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

1. Organization

MyoKardia, Inc. (the “Company”) is a clinical-stage biopharmaceutical company pioneering a precision medicine approach to discover, develop and commercialize targeted therapies for the treatment of serious and neglected rare cardiovascular diseases. The Company’s initial focus is on the treatment of heritable cardiomyopathies, a group of rare, genetically driven forms of heart failure that result from biomechanical defects in cardiac muscle contraction. MyoKardia’s most advanced program, mavacamten, is in four clinical trials, including a pivotal Phase 3 study for the treatment of obstructive hypertrophic cardiomyopathy. A second clinical-stage candidate, MYK-491, is in a Phase 2a multiple-ascending dose study in patients with stable systolic heart failure. The Company was incorporated on June 8, 2012 in Delaware and its corporate headquarters and operations are in South San Francisco, California.

Liquidity

The Company has incurred significant operating losses since inception and has an accumulated deficit of $278.2 million as of June 30, 2019. The Company has relied on its ability to fund its operations through private and public equity financings, and to a lesser extent, through a license and collaboration arrangement with a collaboration partner, Sanofi S.A. (“Sanofi”), via its subsidiary, Aventis Inc. As discussed further in Note 3, the collaboration agreement with Sanofi ended on December 31, 2018 and the Company no longer records revenues from Sanofi nor has it received reimbursements of research and development expenses after June 30, 2019. The Company has not yet received regulatory approval to commercialize or sell any product and does not have customers. Management expects operating losses and negative operating cash flows to continue for the foreseeable future. As the Company continues to incur losses, a transition to profitability is dependent upon the successful development, approval, and commercialization of the Company’s products and product candidates and the achievement of a level of revenues adequate to support its cost structure. The Company’s ultimate success depends on the outcome of its research and development activities. The Company anticipates the need to raise additional capital to fully implement its business plan and intends to raise such capital through the issuance of additional equity, debt and/or strategic alliances with partner companies. There is no assurance that such financing will be available on terms acceptable to the Company, if at all.

On March 8, 2018, the Company filed a Registration Statement on Form S-3ASR (the “2018 Shelf Registration Statement”) covering the potential offering, issuance, and sale of an indeterminate amount of common stock, preferred stock, debt securities, warrants and/or units. In March 2019, the Company completed a follow-on offering under the 2018 Shelf Registration Statement in which the Company issued 5,663,750 shares of common stock at a price of $51.00 per share, including 738,750 shares sold directly to the underwriters upon exercise of their option to purchase up to 738,750 shares of the Company’s common stock within 30 days of the offering. During the six months ended June 30, 2019, the Company received proceeds totaling approximately $271.2 million from the offering, net of underwriting discounts and commissions and offering expenses.

As of June 30, 2019, the Company had $602.4 million of cash, cash equivalents and investments (short-term and long-term) and management believes that these amounts will be sufficient to meet the Company’s anticipated operating and capital expenditure requirements for the twelve months following the issuance date of this Form 10-Q. Management’s belief with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional funding.