Could midday napping save your life? If the experience of Greek men is any guide, the answer just may be yes. In a study released yesterday, researchers at the Harvard School of Public Health and in Athens reported that Greeks who took regular 30-minute napping were 37% less likely to die of heart disease over a six-year period than those who never napped. The scientists tracked more than 23,000 adults, finding that the benefits of napping were most pronounced for working men. Researchers have long recognized that Mediterranean adults die of heart disease at a rate lower than Americans and Northern Europeans. Diets rich in olive oil and other heart-healthy foods have received some of the credit, but scientists have been intrigued by the potential role of napping. The study concluded that napping was more likely than diet or physical activity to lower the incidence of heart attacks and other like-ending heart ailments. Specialists not involved with the study said there are sound biochemical reasons to believe that a nap may help protect against heart disease. Essentially, they said, sleep at any time of day acts like a valve to release the stress of everyday life.