Multiple-lead surface potential maps were compared throughout ventricular activation in nine patients with mild-to-moderate pulmonic stenosis and in 12 patients with mild-to-moderate aortic stenosis. Abnormal patterns of potential distribution were found in aortic stenosis, including three patients without electrocardiographic evidence of left ventricular enlargement. When related to the onset of depolarization, abnormal departures started later, peaked later, lasted longer, and were more intense, more uniform and discrete in aortic stenosis. In pulmonic stenosis, abnormal departures started earlier, but were more dispersed in timing and location than in aortic stenosis. The left ventricle appears to be the more remote, though more powerful and compact, generator. The right ventricular shell, however, is nearer to the surface, and is more anatomically extended in surface area, permitting much wider shifts in wavefront location and orientation as a result of small differences in pressure, or volume, or location of the heart in the thorax.