Fig. 3A. Black and white renditions of the colorgraphic output of the computer simulation of a normal excitation recovery sequence is presented here. The cross sections are selected from the complete set and are at 10 mm intervals. Each is at right angles to the long axis of the left ventricle. Thus each section as viewed from the anterior perspective reveals its underside (see Fig. 2 for orientation). Resting myocardium is dark on these sections. Excitation begins on the left septal surface in the mid portion near the junction with the apical third as shown and progresses rapidly to the endocardium of the left ventricle by 30 ms. It propagates from endocardium to epicardium. The active region at the excitation front is limited to about 3 mm. Recovery is a slower process and is more distributed. The myocardial action potential durations are adjusted in the simulation so that recovery procedes from epicardium to endocardium around the perimeter of the left ventricle. Recovery is just underway at 180 ms, has proceded to the midwall of the left ventricle by 260 ins, and is approaching the subendocardium, the last region to be repolarized.