Given the American diet, and his age, it is a pretty good bet that he has arteriosclerosis. You don’t mention what his cholesterol levels are. That makes a difference. This past spring, during a routine physical, I mentioned my running had become slower and I had less stamina than a year earlier. even though I had just participated in a 10 mile race in almost the same time as the year before, my shorter runs took 10% longer. I had no other symptoms or indications of heart disease, except for consistently high cholesterol levels in the 230— 245 range. My doctor ordered a stress test, and I was found to have “small anomalies.” This was followed by an angiogram. During the angiogram, two arteries were found to be significantly blocked, and stents were inserted. I don’t feel better or different, but my running has improved.