The systolic and diastolic function of the heart of hemodialysis (HD) patients and the effect of intravenous vitamin D therapy on cardiac function was studied by Doppler and digitized M-mode echocardiography in 10 HD patients before and after 3–4.5 months of calcitriol therapy. Calcitriol was administered intravenously 1–3 times a week at a dose of 1–2 µg after the dialysis sessions. Ten age- and sex-matched healthy controls were also examined echocardiographically. Before calcitriol therapy cardiac wall thicknesses (interventricular septum, posterior wall) and left ventricle (LV) dimensions (end diastolic, end systolic) were greater, and LV diastolic (peak late diastolic velocity, peak early diastolic velocity/peak late diastolic velocity ratio, isovolumic relaxation time) and systolic (fractional shortening) function was impaired in HD patients as compared to controls. The LV posterior wall thickness was related to plasma parathyroid hormone (PTH; r = 0.70, p = 0.01) in the patients. Calcitriol therapy raised serum ionized Ca from 1.23±0.04 to 1.33 ± 0.04 mmol/l and reduced PTH from 41.1±10.7 to 34.2±11.7 pmol/l (29±11%). Calcitriol therapy did not cause any significant changes in cardiac function in the whole patient group. However, in a subgroup of 5 patients with severe but controllable hyperparathyroidism (PTH >3 times upper normal margin) the LV dimensions and systolic function improved (LV end systolic dimension from 39.0 ± 4.0 to 31.3 ± 2.9 mm, p = 0.03; LV end diastolic dimension from 57.7 ± 3.1 to 53.4 ± 3.0 mm, p = 0.06; fractional shortening from 33 ± 4 to 42 ± 3%, p = 0.03). The diastolic indices improved also, but not significantly. In conclusion, left ventricle hypertrophy and systolic and diastolic dysfunction was observed in HD patients. Intravenous calcitriol therapy improved cardiac function in patients with severe secondary hyperparathyroidism.