Sudden and staged reperfusion after experimental coronary artery occlusion was studied in relation to recovery of cardiac function and postreperfusion arrhythmias. Eighteen closed chest dogs with 3 hour intracoronary balloon occlusion of the proximal left anterior descending coronary artery were studied using two-dimensional echocardiography over a period of 3 weeks after reperfusion. Nine dogs had sudden reperfusion by abrupt balloon deflation. In nine other dogs reperfusion was staged with partial reflow (20 ml/min) for 2 hours through the central lumen of the catheter during persisting intracoronary balloon inflation, followed by balloon deflation and full reperfusion. Within the first 30 minutes of sudden reperfusion, ischemic zone end-diastolic wall thickness increased significantly, from 6.8 +/- 0.3 mm at 3 hours of occlusion to 10.2 +/- 2.6 mm (p less than 0.05). In contrast, at 30 minutes of partial reflow, wall thickness was 7.5 +/- 0.7 versus 6.8 +/- 0.7 mm at 3 hours of occlusion (NS). A small temporary increase in end-diastolic wall thickness was noted when full reflow was established after 2 hours of staged reperfusion. However, wall thickness was normal on the first day in the staged reperfusion series, while sudden reperfusion delayed recovery to 7 days. Function of the ischemic zone failed to improve substantially until day 3 after sudden reperfusion, whereas it improved consistently starting as early as 30 minutes after institution of the staged reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)