Some of the 1 million Americans hospitalized each year with a dangerous type of chest pain soon may get a "super aspirin" to help prevent them from going on to suffer a heart attack.

The Food and Drug Administration on Thursday approved Merck & Co.'s Aggrastat, a medicine inspired by the venom of an African snake. Merck estimated that if Aggrastat is used widely, it could help prevent up to 40,000 heart attacks and deaths."This is a huge step forward," said Dr. Christopher Cannon, a cardiologist at Brigham & Women's Hospital in Boston.

Unstable angina, a dangerous pain attack, is the leading reason for admitting people to coronary care units. Today, they are treated with aspirin and a blood thinner called heparin, to help stop the formation of blood clots that can trigger heart attacks. Still, 10 percent to 12 percent of patients go on to have a heart attack, and some die, within a month of developing unstable angina.

Aggrastat is the first in a new class of medicines that, given in addition to heparin and aspirin, appears to cut that risk by about a third.

Unstable angina occurs when years of cholesterol buildup on artery walls suddenly causes a rupture. Blood cells called platelets clump around the wound. As the clot becomes larger, it blocks blood flow to the heart.

These cells are held together by a protein called fibrinogen that hooks onto platelets at sites called glycoprotein IIb-IIIa receptors. Aggrastat works by blocking those receptors - thus preventing the fibrinogen from literally gluing together blood clots.

Ironically, Merck modeled the drug on snake venom.

Doctors knew that some snakebite victims bleed to death because the venom contains powerful anti-clotting proteins. Merck and researchers from Temple University isolated one of those proteins from an African snake called the saw-scaled viper. Then Merck literally built the Aggrastat molecule to mimic the snake venom's anti-clotting effect without the toxins.

Having a new class of drug to treat these complex patients is important, said Dr. James Willerson, medical director of cardiology at the Texas Heart Institute. "It's a different kind of inhibitor, and it certainly has appeared to be effective," he said. "It will get wide use."

"It doesn't dissolve blood clots, but it will help prevent them from growing and causing heart attacks," added Cannon, who has tested the drug.

The FDA, which classified Aggrastat as a priority drug, cautioned that the drug does increase a patient's risk of bleeding.