Circulating epinephrine and norepinephrine are avidly absorbed and stored by the heart muscle but not by skeletal muscle of dogs. Stimulation of the cardiac sympathetic nerves augments myocardial norepinephrine but not epinephrine. Sympatholytic drugs do not diminish, some even increase active catecholamines in heart muscle. The results explain a number of pathophysiologic conditions briefly enumerated.