Nutritional deficiency of vitamin D is common in developing countries as a result of both inadequate diet and exposure to ultraviolet light. The most striking biochemical finding in this illness is hypocalcemia. Reduction in serum calcium level may affect ventricular contraction. The purpose of this study was to evaluate prospectively left ventricular function in a group of 27 infants diagnosed as having rickets. Electrocardiograms and echocardiographic studies were undertaken in all patients. A group of ten healthy infants was used as a control for the echocardiographic examinations. Patients were divided into three groups according to the biochemical classification of rickets. There were eight patients in group I, nine in group II, and ten in group III. Abnormal electrocardiographic findings were noted in four infants in group I, three in group II, and six in group III before treatment of the rickets. These changes resolved following treatment. Echocardiographic studies revealed left ventricular dysfunction in the pretreatment stage. The most striking echocardiographic finding is the increase in the ratio of interventricular septal thickness to left ventricular posterior wall thickness in eight patients from group III. This returned to normal after treatment of the rickets. This study has demonstrated echocardiographic evidence of left ventricular dysfunction in children with rickets. These abnormalities were not, however, sufficiently severe to be associated with clinical signs of cardiac failure. Cardiomyopathy may develop in rickets, especially in the third stage of the disease, and this finding may return to normal following adequate treatment of the rickets.