(Reuters) - U.S. health regulators on Wednesday approved Amgen Inc's Corlanor to treat patients with chronic heart failure, giving the world's largest biotechnology company its first cardiovascular product.

The Food and Drug Administration approved the use of Corlanor (ivabradine) on top of current standard of care beta blockers for patients whose symptoms of heart failure are stable and who have a normal heartbeat and a resting heart rate of at least 70 beats per minute.

Chronic heart failure is a common and debilitating condition in which the heart is unable to pump enough blood throughout the body.

"We see in the realm of a million patients in the U.S. who would be in this class and might have a heart rate in the range," Amgen's research chief, Sean Harper, said in an interview.

Amgen acquired U.S. commercial rights to Corlanor from French drugmaker Servier, which sells the medicine in Europe. RBC Capital Markets analyst Michael Yee said that long term Corlanor could become a $500 million a year drug for Amgen. Amgen shares rose 1.3 percent in extended trading following the FDA announcement.

In a large clinical trial comparing Corlanor with a placebo, the drug significantly reduced the risk of rehospitalization, a common and costly event associated with chronic heart failure.

Corlanor decreases the heart rate by blocking a function of the heart's natural pacemaker cells. Heart failure patients tend to have an increased heart rate that can prove harmful over time as the muscle works to compensate for diminished pumping ability.

"Heart failure is a leading cause of death and disability in adults," Norman Stockbridge, director of the FDA's Division of Cardiovascular and Renal Products, said in a statement. "Corlanor ... represents the first approved product in this drug class."

The FDA decision came after a delay following a request for additional clinical data from Amgen.

The most common side effects observed in clinical trial subjects were excessive slowing of the heart rate, high blood pressure, atrial fibrillation, and temporary vision disturbance. Corlanor will be dispensed with a patient medication guide with safety information and instructions for its use, the FDA said.

While Corlanor marks Amgen's entry into cardiovascular medicine, the company is awaiting an approval decision on a much more high profile heart drug with multibillion-dollar sales potential. An FDA decision is expected by late August on Amgen's injectable cholesterol fighter Repatha (evolocumab) from a promising new class of drugs called PCSK9 inhibitors.

(Reporting by Bill Berkrot; Editing by Christian Plumb and Leslie Adler)