Passive transcatheter coronary arterial perfusion, i.e., autoperfusion, has been introduced for clinical use to ameliorate short episodes of myocardial ischemia during percutaneous transluminal coronary angioplasty. The primary goal of this study was to evaluate the cardioprotective effect of autoperfusion after prolonged coronary artery occlusion. Accordingly, in 24 anesthetized dogs, either the left anterior descending or left circumflex coronary artery was occluded for 6 hours. The dogs were randomized to a control group subjected to coronary artery occlusion alone (n = 13) or to a group treated with transcatheter autoperfusion (n = 11). The hypoperfused zone, i.e., risk area and infarct size, were measured by autoradiography and triphenyltetrazolium chloride staining, respectively. The hypoperfused zone was 30 +/- 2% and 29 +/- 2% in the control and treated (NS) groups, respectively. When infarct size was expressed as a percent of the hypoperfused zone, it was 84 +/- 5% in the control group and 25 +/- 9% in the group treated with transcatheter autoperfusion (p less than 0.001), showing a reduction of 70%. In addition, an in vitro study showed pressure-dependent flow during autoperfusion as reflected by close linear relationship between perfusion pressure and flow (Flow = 0.54 X Pressure + 16.16, r = 0.99, n = 16). These data suggest that although passive coronary arterial perfusion for 6 hours after coronary occlusion does not prevent myocardial necrosis, it markedly reduces myocardial infarction in the canine model.