An attempt has been made to uncover the vectorcardiographic spectrum of combined ventricular hypertrophy by studying a group of 82 patients with cyanotic tetralogy of Fallot representing right ventricular hypertrophy with normal or less than normal left ventricular muscle mass and 140 patients with tetralogy of Fallot and surgically created systemic-pulmonary shunts representing right ventricular hypertrophy combined with varying degrees of increased left ventricular muscle mass.An analysis of the spatial orientation of the maximal QRS vectors has demonstrated a continuum of vectorcardiographic patterns. These extend starting with severe right ventricular hypertrophy through a series of ventricular hypertrophy patterns representing right ventricular hypertrophy with progressively increasing left ventricular potentials toward dominant left ventricular hypertrophy patterns of combined ventricular hypertrophy. An estimate of the relative contribution of the two ventricles to a given vectorcardiographic pattern of combined ventricular hypertrophy is possible by analysis of the direction of maximal spatial QRS vectors.