By means of small intramural electrodes, potentials at multiple depths within the ventricular wall were recorded in myocardial infarction and in normal hearts. In 41 animals with coronary artery occlusion, electrocardiographic and histologic correlations indicated that coronary QS waves may represent negative potentials transmitted from viable intramural muscle as well as from the cavity. Coronary QR waves were obtained over transmural infarcts containing a mixture of viable and dead tissue, but not over purely subendocardial lesions. In the normal ventricle, positive depolarization potentials greatly predominated over negative potentials. Clinical applications are discussed.