Cardiovascular complications are an important cause of morbidity and mortality in chronic hemodialysis patients. In order to examine the effect of parathyroid hormone (PTH) and vitamin D on left ventricular functions, 11 patients between the ages of 13 and 18 years on regular hemodialysis were investigated using M-mode echocardiography and systolic time intervals. The ratio of the pre-ejection period to the left ventricular ejection time was found to be 0.38 +/- 0.02 (range (0.25 +/- )>50) and was elevated above normal in five of the 11 patients examined. Four of these patients has hypertension and one had severe anemia. The left ventricular ejection fraction was 55 +/- 2.54% and fractional fiber shortening was 31.55 +/- 2.26%, both of which were within normal limits for age. Although the velocity of circumferential fiber shortening was within normal limits in the majority of cases, the mean value was 1.437 +/- 0.11 circ/s, which is above normal for this age period. PTH levels were between one and 4.70 ng/ml. All of the hemodialysis patients had been receiving 1 alpha hydroxy-cholecalciferol and had normal calcium levels. Although they had high PTH levels, most of these patients displayed normal myocardial contractility. No significant correlation was obtained between increment in PTH levels and myocardial function indices. These results imply that PTH is not the only factor affecting myocardial functions. Since all of these patients have received vitamin D therapy for long periods, we suggest that vitamin D may have prevented the deleterious effect of PTH on myocardial function.