In double outlet left ventricle,both the pulmonary artery and the aortaarisefromthemorphologicleft ventricle. This paper presents the anatomic and cineangiocardiographic features of five patients who had this condition proved at surgery or autopsy. The condition of the first patient was incorrectly diagnosed as transposition of the great arteries with pulmonary stenosis and ventricular septal defect; the anatomic features were correctly interpreted at operation in 1966 and appropriate repair was made, but the patient died postoperatively. The condition of the other four patients was correctly diagnosed. The second patient had Ebstein's malformation of the tricuspid valve and hypoplastic right ventricle in addition to double outlet left ventricle; her condition was not considered operable. Two patients, one with visceroatrial situs solitus, concordant d-loop and dextrocardia, were surgically treated with good long-term results. The fifth patient died 2 years postoperatively and is the first patient reported to have double outlet left ventricle with visceroatrial situs inversus, a discordant d-loop and levocardia. The segmental approach to the classification and diagnosis of connection disorders is discussed and the radiologic criteria by which double outlet left ventricle may be diagnosed considered in detail. The importance of using the radiologic projection (usually left anterior oblique) that profiles the ventricular septum is emphasized because the diagnosis can be established only by delineating the relations of the origins of the great arteries to the ventricular septum. The surgical significance of other anatomic features, including the number, size and position of ventricular septal defects and conal malformations, is also discussed.