Electrocardiograms obtained in two groups of patients with inversion of the ventricles and transposition of the great arteries, were analyzed: group I corresponding in situs solitus and group II to situs inversus. This series comprises 36 cases (29 of group I and 7 of Group II), in which the diagnosis of the main congenital heart disease --ventricular inversion-- and of the associated defects was established by angiocardiography. In 7 cases of group I and in one of group II, the angiocardiographic diagnosis was proved at least in part during open heart surgery. Direct anatomic study was possible in 5 more cases of group I and in 2 more of group II. Each group comprises two subgroups: A, without RBBB, and B, with RBBB of different degrees. Group I consists of 11 cases of subgroup A and 18 of subgroup B. In group II there were 2 cases of subgroup A and 5 of subgroup B. Vectorcardiograms were obtained following Grishman's method in 17 cases of group I (8 of subgroup A and 9 of subgroup B) and in 3 cases of group II (1 of subgroup A and 2 of subgroup B). In 7 cases of group I (5 of subgroup A and 2 of subgroup B), it was possible to record also the vectorcardiographic curves following Frank's method. Electro and vectorcardiographic findings were correlated with hemodynamic data and, in some cases, also with anatomic ones.