Dr. Smith and other cardiologists say the main problem is that there is no way to figure out who has “vulnerable plaques,” those prone to rupture. Researchers are trying to find biomarkers, substances in the blood that can show the presence of these dangerous, ticking time-bomb plaques. So far, no biomarker has proved very accurate.

Mr. Russert’s heart disease was a mixed picture. Some factors looked favorable. There was no family history of heart attacks. Though he had high blood pressure, drugs lowered it pretty well, said his internist, Dr. Michael A. Newman. His total cholesterol was not high, nor was his LDL, the bad type of cholesterol, or his C-reactive protein, a measure of inflammation that is thought to contribute to plaque rupture. He did not smoke. At his last physical, in April, he passed a stress test, and his heart function was good. Dr. Newman estimated his risk of a heart attack in the next 10 years at 5 percent, based on a widely used calculator.

On the negative side, Mr. Russert had low HDL, the protective cholesterol, and high triglycerides. He was quite overweight; a waist more than 40 inches in men increases heart risk. A CT scan of his coronary arteries in 1998 gave a calcium score of 210, indicating artery disease  healthy arteries do not have calcium deposits  and a moderate to high risk of a heart attack. An echocardiogram in April found that the main heart pumping chamber had thickened, his ability to exercise had decreased slightly, and his blood pressure had increased a bit. Dr. Newman and his cardiologist, Dr. George Bren, changed his blood pressure medicines, and the pressure lowered to 120/80, Dr. Newman said.

Another blood test, for a substance called apoB, might have been a better measure of risk than LDL, some doctors say. Others disagree.

Some doctors say people like Mr. Russert, with no symptoms but risk factors like a thickened heart, should have angiograms, in which a catheter is threaded into the coronary arteries, dye is injected, and X-rays are taken to look for blockages. Some advocate less invasive CT angiograms. Both types of angiogram can identify plaque deposits, and if extensive disease or blockages at critical points are found, a bypass is usually recommended. But the tests still cannot tell if plaques are likely to rupture, Dr. Smith and other cardiologists say. And Mr. Russert’s doctors did not think that an angiogram was needed.

An autopsy found, in addition to the plaque rupture, extensive disease in Mr. Russert’s coronary arteries, enough to surprise his doctors, they said. Had they found it before, Dr Newman said, a bypass would have been recommended. Dr. Bren differed, saying many cardiologists would still not have advised surgery.