Patients with the condition, referred to as ACS, have had heart attacks or chest pains that indicate the risk of a heart attack. Their condition is usually caused by blocked coronary arteries and an estimated 1 million people a year in the United States are hospitalized after having an ACS episode.

A panel of outside medical experts to the U.S. Food and Drug Administration last month recommended against approval of Xarelto for the new indication. The panel said the pill looked promising, but expressed concern about missing clinical-trial data and bleeding risks.

Xarelto was approved in the United States late last year to prevent strokes among patients with an irregular heartbeat called atrial fibrillation that is most common among the elderly. It is also approved to reduce risk of blood clots in the legs and lungs of people who have had knee or hip replacement surgery.

J&J, which developed the drug in partnership with German drugmaker Bayer AG, said it is evaluating the FDA's response, known as a complete response letter.

"We will continue to work with the FDA to fully address their questions as quickly as possible," said Dr. Paul Burton, the cardiovascular franchise medical leader at Janssen R&D, the division of Johnson & Johnson that makes Xarelto.

Xarelto is one of three new medicines that offer potential advantages over older drugs to prevent strokes and other dangerous conditions caused by blood clots. Investors have tried to bet on which of the three will become dominant in a race between Xarelto, Eliquis from Pfizer Inc and Bristol-Myers Squibb Co, and Pradaxa from private German drugmaker Boehringer Ingelheim.

Pradaxa gained U.S. approval in 2010 for use in atrial fibrillation, while Eliquis is still under FDA review, with a decision expected by the end of June.

But Xarelto's rivals failed in treating patients with ACS, and an approval for those patients would have given Bayer and J&J a potentially distinct market.

(Reporting by Ransdell Pierson in New York and Anna Yukhananov in Washington; editing by Andre Grenon)

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