A new and emerging understanding of how heart attacks occur indicates that increasingly popular aggressive treatments may be doing little or nothing to prevent them.

The artery-opening methods such as bypass surgery and stents, the widely used wire cages that hold plaque against an artery wall -- can open obstructed blood vessels and alleviate crushing chest pain. Stents can also rescue someone in the midst of a heart attack by destroying an obstruction and holding the artery open.

But the new model of heart disease shows that a vast majority of heart attacks do not originate with artery obstructions.

Instead, recent and continuing studies show that a more powerful way to prevent heart attacks in patients at high risk is to adhere rigorously to what can seem like boring old advice -- give up smoking, for example, and take drugs to control blood pressure, drive cholesterol levels down and prevent blood clotting.

Researchers estimate that just one of those tactics -- lowering cholesterol to what guidelines suggest can reduce the risk of heart attacks by a third, but is followed by only 20% of heart patients.

''It's amazing, and it's completely backward in terms of prioritization,'' said Dr. David Brown, a cardiologist at Beth Israel Medical Center in New York.

Heart experts say they understand the disconnect: They, too, at first found it hard to believe what research was telling them. For years, they were wedded to the wrong model of heart disease.

''There has been a culture in cardiology that the narrowings were the problem and that if you fix them the patient does better,'' said Dr. David Waters, a cardiologist at the University of California.

But, researchers say, most heart attacks do not occur because an artery is narrowed by plaque. Instead, they say, heart attacks occur when an area of plaque bursts, a clot forms over the area and blood flow is abruptly blocked. In 75% to 80% of cases, the plaque that erupted was not obstructing an artery and would not be stented or bypassed. The dangerous plaque is soft and fragile, produces no symptoms and would not be seen as an obstruction to blood flow.

Heart patients have hundreds of vulnerable plaques, so preventing heart attacks means going after all their arteries by attacking the disease itself. That is what happens when patients take drugs to lower their cholesterol levels, to control their blood and to prevent blood clots. Yet, researchers say, old notions persist.