ORLANDO, Fla. – Adding Plavix to other anti-clotting drugs typically given to heart attack patients saves lives and prevents second heart attacks, two huge international studies found.

The strategy is the first big advance in heart attack care in more than a decade, since modern clot-busters were shown to work, specialists said.

This cheap and simple treatment will have a big impact in the nation’s community hospitals, where most Americans get care, they said. It could also help in developing countries where heart surgery and procedures to open blocked arteries are uncommon.

“It really is a great day for heart attack patients,” said one of the researchers, Dr. Christopher Cannon of Harvard Medical School.

The results of the two studies were presented yesterday at an American College of Cardiology conference in Or lando. One of the studies also was published online by the New England Journal of Medicine and will be in its March 24 print edition.

The studies looked at heart attacks caused by a large clot that fully or almost completely blocks a major artery – the type that accounts for about a third of the 865,000 heart attacks each year in America and the 10 million worldwide.

These patients can be treated with emergency procedures to open the artery or with medications to dissolve the clot until they can be given an angiogram to see whether they need surgery or angioplasty. But arteries reclose about one-fourth of the time in people given medications, doubling their risk of dying before a procedure can be done.

Plavix already is used to prevent clotting, but its safety and effectiveness for treating major heart attacks while they are happening had not been tested until now. The two studies were funded by the companies that sell Plavix – Sanofi-Aventis and Bristol-Myers Squibb. Many of the researchers have consulted for the companies.

One study, involving about 46,000 heart attack patients in China, found that the risk of death, stroke, or another heart attack was 9% lower in patients given Plavix along with standard anti-clotting drugs – aspirin, heparin, and the clot-busters TPA or streptokinase – than in those who got the standard drugs alone.

The risks of bleeding and other serious side effects were no different.

“The treatment was very effective and very safe,” said Dr. Zhengming Chen of the University of Oxford in England, who led the Chinese study.

Two weeks of Plavix pills cost $50 to $100 a patient. For every million heart attack patients treated this way, 5,000 deaths and another 5,000 major heart problems or strokes would be prevented, Dr. Chen said.

The other study was led by Dr. Marc Sabatine of Harvard and the Brigham and Women’s Hospital in Boston and involved 3,491 heart attack patients in Europe given standard drugs with or without Plavix. The risk of death, another heart attack, or artery reclogging was 21.7% in those on standard drugs alone but only 15% among those given Plavix. This amounted to a 36% lower risk for those taking Plavix.

Doctors also found that Plavix appeared to be safe even for patients about to have heart bypass surgery. This is good news because surgeons are reluctant to operate on people who recently received the drug, for fear it will cause excessive bleeding.

Indeed, President Clinton’s doctors cited his Plavix treatment as a reason they delayed his bypass surgery a few days last summer.

In an editorial in the New England Journal, doctors from Johns Hopkins University in Baltimore and the University of Texas Southwestern Medical Center in Dallas said that the results may have been particularly rosy in the European study because patients generally had a lower risk than most heart attack sufferers.

The study also did not include elderly and thin people, who have a higher risk of bleeding from some anti-clotting and blood-thinning treatments.

But because aspirin does not work in many people, finding that a different anti-clotting drug like Plavix works is good news, they said.

In other news at the conference, an analysis involving the patients in the Chinese study found that the common practice of giving heart attack patients drugs called beta-blockers should be delayed. People given the drug had fewer repeat heart attacks but more risk of heart shock, so the risks and benefits canceled each other out.