Left heart volume characteristics were evaluated by using biplane cineangiocardiography in 18 studies in 15 patients with total anomalous pulmonary venous connection (TAPVC) and in 37 studies on 35 patients with large secundum or sinus venosus atrial septal defects (ASD). Left ventricular end-diastolic volume (LVEDV) was decreased to less than 67% of normal in five of 15 preoperative TAPVC patients, but the average value for the entire group was not significantly different from normal. In ASD patients, the average LVEDV was 87% of normal which was significantly decreased (P< 0.001). The ejection fraction was decreased from normal in patients with TAPVC and ASD who were less than 2 years of age (0.62 vs. 0.68,P< 0.01), but was normal in older patients. Left ventricular systolic output was significantly decreased from normal in both TAPVC (75% of normal,P< 0.001) and ASD patients (81% of normal,P< 0.001). Left atrial maximal volume was significantly decreased from normal in TAPVC patients averaging only 55% of normal (P< 0.001), but was normal in eight ASD patients. All volume variables increased following corrective surgery in two TAPVC patients and two ASD patients. These studies document that left heart volumes and outputs in infants and children with TAPVC and large isolated atrial defects can be diminished preoperatively.