Septation of a single ventricle into 2 functioning ventricles can provide an alternative to the Fontan operation. However, early experiences with septation reported unacceptable morbidity and mortality. The present study selected only those patients with large volume-overloaded hearts, 2 well-functioning atrioventricular valves, and an absence of severe outlet obstruction. Early and intermediate outcomes are evaluated.Between June 1990 and March 1999, 11 patients underwent septation in 1 or 2 stages. Diagnoses of the patients included double-inlet left ventricle in 9, double-inlet right ventricle in 1 patient, and indeterminate ventricle in 1 patient. Five had l-transposition and 3 had d-transposition of the great arteries. Six had septation as 1 stage, 5 as planned 2-stage operations (2/5 completed). The median age for septation in 1 stage was 2.1 years (range 4 months to 5.8 years); for 2 stages, the median age was 7.2 months (range 3 to 14 months). Median follow-up time was 2.3 years. Eight of 11 patients survived (73%), with 2 early deaths and 1 late death. Seven of the 8 survivors have undergone complete septation (5 as single stage, 2 as 2 stages). Complications included surgically induced complete atrioventricular block in 1 patient and significant residual ventricular septal defects in another. Qualitatively, left ventricular function by echocardiography is normal in all patients, whereas right ventricular function is mildly decreased in 1 patient. All patients are clinically well.The septation procedure for single ventricle hearts may be a reasonable alternative to the Fontan operation in selected patients.