Systolic time intervals (STI) were evaluated in 19 female patients with uncomplicated ostium secundum atrial septal defect (ASD), before, shortly after (within 2 months) and a long time after the corrective surgery (mean 13.2 years). The measurements were obtained from simultaneous high speed photographic recordings of electrocardiogram, external carotid pulse and phonocardiogram. Before the operation, a significant prolongation of Q-I heart sound interval was detected, together with a less prominent but statistically significant shortening of the left ventricular ejection time; the above alterations were not correlated with the magnitude of the shunt and disappeared shortly after corrective surgery. The STI were still normal a long time after surgical closure of ASD. In accordance with hemodynamic studies reported by other authors, our results confirm that the deviations of STI observed in ASD are due to a reduced diastolic filling of the left ventricle secondary to an apparent decreased distensibility.