During thoracotomy 12 anesthetized swine were instrumented and valvuloplasty catheters were positioned at the aortic anulus. Thirty-second occlusions of the left ventricular outflow tract were performed with a single catheter (n = 34) and with simultaneous inflation of dual catheters (n = 47). Left anterior descending coronary artery blood flow fell to minimums of 15% of baseline flow (SD 13.9%) during single balloon occlusion and to 63.8% of baseline flow (SD 22.8%) during dual balloon occlusion. Main pulmonary artery flow fell to minimums of 13.6% of baseline flow (SD 17.3%) during single balloon occlusion and to 66.9% of baseline flow (SD 18.3%) during dual balloon occlusion. Femoral artery systolic pressure dropped to 20.1% of baseline pressure (SD 5.6%) during single balloon occlusion and to 82.6% of baseline pressure (SD 8.1%) during dual balloon occlusion. During single balloon occlusion, 8.5 (SD 3.5) premature ventricular contractions were observed and 2.8 (SD 1.6) premature ventricular contractions occurred during dual balloon occlusion. After deflation of the valvuloplasty catheters, the time to return of baseline flow in the left anterior descending coronary artery was 28.4 second (SD 23.2 seconds) with the single balloon method and 4.8 seconds (SD 3.7 seconds) with the dual balloon method. All of these differences were statistically significant (p less than .001). During occlusion of the left ventricular outflow tract by dual valvuloplasty catheters, there were better hemodynamics, higher coronary blood flows, and fewer premature ventricular contractions than during occlusion by a single catheter. After occlusion by dual catheters, returns to baseline coronary flows were more rapid than after single catheter occlusions. These data may have application to clinical aortic valvuloplasty.