The masters step in--see also Nathan Pritikin, below--to find a lesson in Jim Fixx's death while running. Both Cooper and Pritikin were acquainted with Fixx and familiar with his habits; Cooper also examines the immediate circumstances of his death. And just as Pritikin's findings reflect his major concern--diet--Cooper's reflect his concern with the proper design of the exercise regimen. Cooper also acknowledges the role of diet and, from the outset, explodes the myths of runners' invulnerability (""Myth #1: I Couldn't Have Heart Disease and Run the Way I Run Without Symptoms""). On the basis of the Fixx case, he cautions runners to get a physician's clearance before beginning a program, and periodically thereafter--and to pay attention to the results. (Fixx seems to have ignored numerous warning signals of heart disease.) Then, be sure that any aerobic exercise program has a warm-up and cool-down component--never stop abruptly. Be alert, moreover, for signs of overstraining or exhaustion, and be willing to rest. Cooper backs all this with a clear comprehensible explanation of what heart attack and sudden death are, and who is especially at risk. The book is at once comforting and realistic: there are real risks, and real preventive steps to take. This is the best kind of help that the Fixx tragedy can provide--athletes will find both Cooper's and Pritikin's guides of benefit.