Company: CYTK
Filing Date: 2025-08-07
Form Type: S-8
Source: 0001193125-25-175412
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Company: CYTOKINETICS INC
Filing Date: 2025-08-07
Form: S-8
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As filed with the Securities and Exchange Commission on August 7, 2025 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-8 REGISTRATION STATEMENT Under The Securities Act of 1933 CYTOKINETICS, INCORPORATED (Exact name of Registrant as specified in its charter)

| Delaware                        |     | 94-3291317            |
| (State or other jurisdiction of 
 incorporation or organization)  |     | -I.R.S. Employer      
 Identification Number |

350 Oyster Point Boulevard South San Francisco, CA 94080 (Address of principal executive offices) AMENDED AND RESTATED 2004 EQUITY INCENTIVE PLAN (Full title of the plan) Robert I. Blum President and Chief Executive Officer Cytokinetics, Incorporated 350 Oyster Point Boulevard South San Francisco, CA 94080 (650) 624-3000 (Name, address, and telephone number, including area code, of agent for service) Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-acceleratedfiler, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2of the Exchange Act.

| Large accelerated filer |     | ☒ |     | Accelerated filer         |     | ☐ |
| Non-accelerated filer   |     | ☐ |     | Smaller reporting company |     | ☐ |
|                         |     |   |     | Emerging growth company   |     | ☐ |

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

EXPLANATORY NOTE This Registration Statement on Form S-8is being filed for the purpose of registering an additional 5,000,000 shares of the Common Stock to be issued pursuant to the Amended and Restated 2004 Equity Incentive Plan (the “EIP”). The shares of the Common Stock previously reserved for issuance under the EIP were registered on the Registrant’s Registration Statements on Form S-8previously filed with the