April 7 (Reuters) - The U.S Food and Drug Administration approved Abiomed Inc's heart pump to treat patients who suffer cardiac shock after heart attack or heart surgery, sending its shares up about 4 percent in extended trading.

Cardiac shock is a life-threatening emergency condition where the heart is suddenly unable to pump enough blood and oxygen to support the body's vital organs. The condition is rare, but is often fatal if not treated immediately.

The most common cause of the shock is damage to the heart muscles from a severe heart attack. On an average, only about 7 percent of people who have heart attacks develop the condition, according to the National Institutes of Health.

Abiomed's Impella heart pumps were first approved earlier in 2008 to maintain blood flow through the body during heart surgeries.

Impella had worldwide sales of about 81 million for the quarter ended Dec. 31. That accounted for about 94 percent of the company's total revenue in the third quarter.

Abiomed's shares were trading up 4 percent at $99.90 after the bell.

(Reporting by Rosmi Shaji in Bengaluru; Editing by Shounak Dasgupta)