A new autoperfusion balloon angioplasty catheter with sideholes proximal and distal to the balloon--facilitating distal blood flow during inflation--was compared with standard angioplasty catheters in a prospective, randomized study with blinded data analysis. Hemodynamic and electrocardiographic markers of ischemia after 1 minute of standard or autoperfusion catheter inflations were compared with ischemia after control inflation with standard balloons. In the patient group randomized to standard balloon inflation only, ST-segment elevation after control inflation with a standard balloon catheter was 0.37 +/- 0.04 mV; ST-segment elevation after final balloon inflation with a standard catheter was unchanged at 0.35 +/- 0.04 mV (difference not significant). In the group randomized to the autoperfusion catheter, control inflation with a standard catheter resulted in 0.48 +/- 0.1 mV ST elevation; final inflation with the autoperfusion catheter demonstrated 0.16 +/- 0.09 mV ST elevation (p less than 0.005). Autoperfusion catheter inflation was continued for 2 minutes without change in electrocardiographic findings: ST segments remained at 0.08 +/- 0.03 mV, unchanged from 0.07 +/- 0.03 mV before angioplasty (difference not significant). Thus, while coronary angioplasty performed with standard catheters resulted in marked ST-segment elevation, in patients undergoing angioplasty with the autoperfusion catheter, ischemia was generally not seen, despite sustained balloon inflation for 2 minutes.