The heart responds positively to programs of chronic dynamic exercise. Hallmark adaptations of the heart include a training bradycardia, increases in end-diastolic dimension and maximal stroke volume, and a general improvement in ventricular performance and contractile function. Of considerable clinical significance are the general observations that chronic exercise renders the myocardium less susceptible to the deleterious effects of acute ischemic episodes and can effectively prevent and/or reverse many of the cardiac functional deficits that are known to occur in settings of chronic hypertension, advanced age, and myocardial infarction. In the text that follows, information gathered over the last 25 to 30 years has been reviewed in an attempt to identify cellular myocardial adaptations, both known and hypothetical, that are responsible for the observed effects of chronic dynamic exercise on the function and morphology of the heart in both normal and selected pathophysiologic settings. Finally, a variety of unresolved issues regarding the ability of chronic exercise to elicit adaptive cardiocyte responses has been identified. In so doing, it is hoped that creative thought and future work in the area will be stimulated.