Both men had ample warning they were prime candidates for heart attacks. Russert had been diagnosed with coronary artery disease, his doctor told MSNBC. Fixx had a terrifying family history, including a father who had a fatal heart attack in his early 40s.

And both took steps to reduce their odds of the same fate. Russert's doctor, Michael Newman, prescribed medication and exercise. He told MSNBC that Russert performed well on a stress test in April. Fixx, who reached the height of his fame before cholesterol-lowering drugs were widely available, changed his diet, laced up his running shoes and ate up the miles.