THOUSAND OAKS, Calif. (AP) — Amgen Inc. is paying Cytokinetics Inc. $50 million as part of an option to exercise rights to a developing heart drug. The payment amounts to more than South San Francisco, Calif.-based Cytokinetics has made in combined revenue over the last three years. Amgen is exercising its option to obtain exclusive worldwide rights to part of Cytokinetics' heart drug program, which includes CK-1827452, a potential treatment for heart failure. The rights option excludes Japan. The companies have been collaborating since 2006.