Regional diastolic wall motion was studied with sonomicrometry in 30 open chest anaesthetised dogs after left anterior descending stenosis or occlusion. Post-systolic shortening and thickening, defined as the magnitude of segment shortening or wall thickening that occurred after end systole, was measured in peripheral and central ischaemic segments. These post-systolic events developed concurrently with impaired systolic shortening or thickening, either immediately after acute coronary occlusion or during progressive stenosis, and persisted with the development of dyskinesis and during reperfusion. The magnitude of these events in dyskinetic segments of 24 dogs was considerable, reaching 50(2)% (mean(SEM)) and 33(3)% of shortening or thickening that was present before coronary occlusion. Post-systolic shortening and thickening were maximum at 100(2) ms after peak negative dP/dt. Significant correlations were found between systolic shortening or thickening before coronary occlusion and post-systolic shortening (r = 0.74, 56 segments) or thickening (r = 0.84, 19 segments) after occlusion, but there was no correlation between post-systolic shortening or thickening and dyskinetic lengthening or thinning. In seven dogs followed for 4 h after coronary occlusion post-systolic shortening fell by 15% in peripheral segments and by 70% in central segments (p less than 0.002). In 17 dogs reperfused after 60 (n = 9) or 90 (n = 8) min of coronary occlusion the maximal recovery of systolic shortening early after reperfusion was significantly related to the magnitude of post-systolic shortening immediately before reperfusion (60 min occlusion r = 0.84, 90 min occlusion r = 0.88). These data show that post-systolic shortening is a marker of potential for early recovery of function of acutely ischaemic myocardium and suggest that it is due, at least in part, to an active process.