Sixteen patients with secundum atrial defect were catheterized giving emphasis to the analysis of the left ventricle at end systole and mid-ejection. The mean ejection fraction of the group was subnormal 57 + 8% when compared with 30 normal patients (71 + 109) P less than .005. Eight patients showed elevated end-diastolic volumes (156 + 10cc) when compared to our normal group (95% + 10cc) P less than .005. A total of 32 hypokinetic and 35 tardokinetic areas were found. Eight patients were restudied after nitroglycerin (0.4 mg sublingually) with an improvement in the ejection fraction from 54% to 70% (P less than .005) and normalization of most of the hypokinetic areas. No correlation was found between total ejection fraction or total systolic wall motion and the shunt size. Probably these left ventricular wall motion abnormalities are primary and not due to the shunt size.