The sequential chamber analysis and angiographic, hemodynamic and clinical features, including those seen on electrocardiography, are presented in 18 patients with a univentricular heart of right ventricular type. In all cases a main chamber with a right ventricular trabecular pattern received both (or the sole) atrioventricular (A-V) connections, and a rudimentary chamber with a left ventricular trabecular pattern receiving no A-V connection was also present. The 18 patients were seen between 1971 and 1979; 6 died and the diagnosis was confirmed at autopsy. Twelve patients had double inlet, four absent right and two absent left A-V connections. Electrocardiography revealed right ventricular hypertrophy in all, and 11 had a superior mean frontal QRS axis. Chest roentgenography disclosed dextrocardia in 7 and levocardia in 11. Of 12 infants presenting with a marked decrease in pulmonary flow, 10 presented as ill neonates with hypoxia and acidosis. Four infants with increased pulmonary flow presented before 8 weeks with heart failure and mild cyanosis. Two with moderate pulmonary stenosis had mild cyanosis, but were asymptomatic. All had associated cardiac anomalies, pulmonary stenosis and persistent ductus arteriosus being the most common. For accurate diagnosis, angiographic demonstration of a posterior rudimentary chamber in addition to the main chamber of right ventricular trabecular pattern is mandatory.