Problems associated with the early evolution of corrective operation (septation) for univentricular heart (single or common ventricle) are illustrated in a total experience of 36 such operations, 30 of which were recent. Complete heart block existed preoperatively in five of the 30 patients and developed at operation in another 10; only two of these 15 patients attained a satisfactory result. Associated pulmonary stenosis was present in 16 patients, and this seemed to influence the result favorably. An extracardiac conduit between the right-sided ventricular chamber and the distal pulmonary trunk was employed in 20 patients. The presence of associated anomalies, including function of the atrioventricular valves in seven, had a highly unfavorable influence on the result. Although all seven of the most favorable candidates attained a satisfactory result, only 13 (43 percent) in the total group of 30 attained a satisfactory result. Further evolution of this operation, as in previous operations for complex congenital heart disease, should provide more results that are satisfactory.