Most patients describe symptoms as discomfort in the chest that may, or may not, radiate into the arms or neck, the back, the jaw, or the stomach. Many also have nausea or shortness of breath. Or they break out in a cold sweat or have a feeling of anxiety or impending doom or have blue lips or hands or feet or feel a sudden exhaustion.

But symptoms often are less distinctive in elderly patients, especially women. Their only sign may be a sudden feeling of exhaustion just walking across a room. Some say they broke out in a sweat. Afterward, they may recall a feeling of pressure in their chest or pain radiating from their chest but at the time, they say, they paid little attention.

Patients with diabetes might have no obvious symptoms at all other than sudden, extreme fatigue.

"I say to patients, 'Be alert to the possibility that you may be short of breath,'" said Dr. Elliott Antman, director of the coronary care unit at Brigham and Women's Hospital. "Every day you walk down your driveway to go to your mailbox. If you discover one day that you can only walk halfway there, you are so fatigued that you can't walk another foot, I want to hear about that. You might be having a heart attack."

Other times, said Dr. George Sopko, a cardiologist at the National Heart, Lung and Blood Institute, symptoms like pressure in the chest come and go. That is because a blood clot blocking an artery is breaking up a bit, reforming, breaking and reforming.

"It's a pre-heart attack," Sopko said. A blood vessel is on its way to being completely blocked. "You need to call 911."

But most people — often hoping it is not a heart attack, wondering if their symptoms will fade, not wanting to be alarmist — hesitate far too long before calling for help.

"The single biggest delay is from the onset of symptoms and calling 911," said Dr. Bernard Gersh, a cardiologist at the Mayo Clinic. "The average time is 111 minutes, and it hasn't changed in 10 years."

At least half of all patients never call an ambulance. Instead, in the throes of a heart attack, they drive themselves to the emergency room or are driven there by a friend or family member. Or they take a taxi. Or they walk.

Patients often say they were embarrassed by the thought of an ambulance arriving at their door. It is an understandable response, but one that can be fatal, cardiologists say.

There may be false alarms, Sopko said: "But it is better to be checked out and find out it's not a problem than to have a problem and not have the therapy."

The right treatment

There also is the question of how, or even whether, the patient gets either of two types of treatment to open the blocked arteries, known as reperfusion therapy.

One is to open arteries with a clot-dissolving drug like tPA, for tissue plasminogen activator.