Bristol-Myers Squibb Co. will buy MyoKardia Inc. for $13.1 billion in cash in a deal to expand its offering of heart drugs.

Bristol-Myers will pay $225 a share, according to a statement from the companies, a premium of 61% over the stock’s Friday closing price. MyoKardia rose 59% in premarket U.S. trading.

With the purchase, Bristol-Myers gets access to MyoKardia’s lead product mavacamten, an experimental drug that treats obstructive hypertrophic cardiomyopathy. Expanding Bristol-Myers’s lineup of heart drugs would help the maker of Opdivo for cancer diversify beyond oncology, an area where much of the industry has focused in recent years.

An application for approval of mavacamten is expected to be submitted in the first quarter of next year, according to the statement. Bristol-Myers plans to explore other uses for the drug and to develop additional experimental compounds from MyoKardia.

Hypertrophic cardiomyopathy is a chronic condition in which the heart muscle becomes abnormally thick, making it harder for the organ to pump blood. It’s estimated to affect about one in 500 people, according to the statement.

Bristol-Myers said it plans to finance the acquisition with a combination of cash and debt.