In 1936 Taussig said that, to the best of her knowledge, among patients with cyanotic heart disease, the only malformation that was associated with left axis deviation in the electrocardiogram was a diminutive or absent right ventricle. She reported one case of tricuspid atresia and another of pulmonary atresia with a closed ventricular septum, in each of which the cardiogram showed left axis deviation. Cleland et al. (1957) thought that the association of central cyanosis with left axis deviation was virtually pathognomonic of tricuspid atresia. Astley, Oldham, and Parsons (1953) and Scott (1955) agreed with others that left ventricular preponderance or much left axis deviation in cyanotic heart disease was almost always diagnostic of tricuspid atresia with a rudimentary right ventricle. There are, however, many exceptions. Wood (1942) reported a case of pulmonary stenosis with a closed ventricular septum and an atrial septal defect associated with central cyanosis: there was left axis deviation and at necropsy the left ventricle was found to be enlarged. Gasul, Richmond, and Krakower (1949) reported a case of Fallot's tetralogy with a patent foramen ovale which was also associated with left ventricular hypertrophy and left axis deviation. Portillo et al. (1959) reported a case that was diagnosed as tricuspid atresia because of the combination of severe central cyanosis and left axis deviation; but at necropsy the patient was found to have Fallot's tetralogy. Soloff (1949) reported a cyanosed baby who died at the age of 2 weeks: there was left axis deviation and at necropsy there was aortic atresia associated with hypoplasia of the left ventricle and gross enlargement of the right ventricle. Uhl (1952) reported another case of a cyanosed baby who died at the age of 7 months, whose cardiogram on one occasion suggested left ventricular hypertrophy: at necropsy almost complete absence of the myocardium of the right ventricle was found, but no intracardiac defect was found to account for the central cyanosis.More recently, however, patients with conditions other than tricuspid atresia, who had central cyanosis and cardiograms with left axis deviation, left ventricular preponderance, or both, have been reported. Shaher (1963) have shown that the cardiogram in single ventricle often shows a pattern of left ventricular dominance as well as left axis deviation. Pung, Gottstein, and Hirsch (1955) noted that left ventricular preponderance had been present throughout the life of a deeply cyanosed boy who died at the age of 18 years and who proved at autopsy to have transposition of the great vessels with a closed ventricular septum and pulmonary infundibular stenosis. Keith, Rowe, and VIad (1958) found that left ventricular dominance in cases of transposition of the great vessels indicated tricuspid atresia or an overriding tricuspid valve.In a recent review of complete transposition of the great vessels, Noonan et al. (1960) have added transposition with a ventricular septal defect and a large pulmonary blood flow to t...