The incidence of pulmonary perfusion defects after routine cardiac catheterization was assessed in 56 patients by comparing ventilation-perfusion (V/Q) lung scans obtained before and 1 day after catheterization. Patients were prospectively randomized in two groups, one in which the brachial approach was performed using an antecubital cutdown procedure, and one in which the percutaneous femoral approach was used. None of the patients with the brachial approach had any ventilation-perfusion mismatch on the V/Q scan; however, three patients (8.3%) with the femoral approach did. These two groups did not differ significantly in clinical characteristics, duration of catheterization, and hemodynamic variables. The data suggest that pulmonary emboli postcardiac catheterization is more frequent in the femoral than the brachial approach. Furthermore, since those pulmonary emboli are mostly asymptomatic, their clinical recognition would be underestimated.