Doctors routinely perform a procedure known as angioplasty on people who have had heart attacks. The procedure involves inserting a tiny balloon into an artery and inflating it to clear blockages that caused the attack. A small mesh tube is inserted to prop the artery open. The procedure can save lives if performed right after a heart attack. But it has been unclear whether the procedure helps patients if done later.

In the biggest, longest study to examine that question, Judith Hochman of the New York University School of Medicine and her colleagues studied 2,166 patients who were treated in 27 countries, three to 28 days after a heart attack.

There was no significant difference between the patients who underwent the procedure and those who received only drug treatment in terms of their death rate or their chance of having a heart attack or experiencing heart failure, the researchers found. In fact, there was some suggestion that those who underwent the procedure may have been more likely to have another heart attack.

It could be that reopening a large clogged artery causes smaller vessels to close, making them unavailable if the large artery gets blocked again, the researchers said.

"These results challenge the long-standing belief that opening a blocked artery is always good. Instead, the study suggests that late angioplasty is unnecessary in this cir*****stance," said Elizabeth G. Nabel of the National Heart, Lung, and Blood Institute, which funded the study.

The results were published online by the New England Journal of Medicine to coincide with their presentation at a meeting of the American Heart Association in Chicago.