Left main coronary angioplasty is associated with high risk because of interruption of blood flow to much of the left ventricle during balloon inflation. An "autoperfusion" balloon angioplasty catheter that allows blood to flow passively distal to an inflated balloon was tested in dogs and compared with inflations with standard balloon catheters. During 3 min occlusions of the left main coronary artery with the autoperfusion catheter, regional myocardial blood flow was preserved at 0.60 +/- 0.14 ml/min/g, compared with 0.07 +/- 0.03 ml/min/g during inflation with standard balloon catheters (P less than 0.01). Similarly, at the end of 3 min of inflation, left ventricular systolic pressure and dP/dt were maintained with autoperfusion catheter inflation, but they were severely depressed after standard angioplasty balloon inflation. All seven dogs survived autoperfusion balloon inflation, whereas five of seven developed sustained ventricular tachycardia and/or ventricular fibrillation during or after standard balloon inflation. Thus, distal blood flow, hemodynamics, and survival were preserved during autoperfusion balloon inflation in the left main coronary artery.