To investigate whether hypocalcemia affects cardiac performance in uremic patients, we studied the hemodynamic changes with short- and long-term correction of hypocalcemia in 4 uremic patients on dialysis using continuous wave Doppler study. At rest, 1 h of intravenous calcium infusion increased calcium level from 1.74 ± 0.17 to 1.92 ± 0.16 mmol/l (p < 0.05). Cardiac output represented by minute distance increased from 10.5 ± 2.0 to 12.1 ± 2.5 m (p < 0.05), but heart rate and blood pressure were unchanged. The peak velocity and acceleration of ascending aortic blood flow increased during calcium infusion. With long-term replacement, calcium level increased from 1.74 ± 0.17 to 1.94 ± 0.15 mmol/l (p < 0.05), but resting hemodynamics were unchanged. On exercise testing, exercise duration increased from 10.6 ± 1.6 min to 12.9 ± 1.5 min (p < 0.01), but hemodynamic parameters at peak exercise were similar. We conclude that acute calcium replacement enhanced cardiac contractility in uremic patients, but cardiac performance at rest and peak hxercise was not improved with long-term therapy. This reflects different cardiac responses to acute versus chronic calcium replacement.