Amgen Inc. said Tuesday that it will pay its partner Cytokinetics Inc. $50 million for rights to its heart-drug program, which includes a promising experimental heart-failure drug.

Amgen in Thousand Oaks and Cytokinetics in South San Francisco have been collaborating since 2006. Cytokinetics’ drug called CK-1827452, which is in mid-stage clinical trials, is the first in a new group of medicines that can increase duration of each contraction of the heart muscle. This can pump more blood through the body without increasing a person? heart rate, which often occurs in older heart-failure medicines.

?K-1827452, with its novel mechanism of action, has potential utility in the treatment of heart-failure patients around the world,?Dr. Roger M. Perlmutter, Amgen? executive vice president for research and development, said in a statement. ?e intend to move this molecule forward rapidly into larger and more definitive clinical trials.

Amgen is paying Cytokinetics a non-refundable exercise fee of $50 million and assumed responsibility for development and worldwide commercialization of the drug, except in the Japanese market. Cytokinetics is eligible for additional money depending on the drug? success. Amgen earlier paid the company approximately $75 million to establish the partnership.

Amgen shares were up 81 cents, or 1.6 percent, to $50.11 in midday trading on the Nasdaq.