The possible association of increased left ventricular ejection fraction (LVEF) in patients with increased serum Ca(2+) was observed in our clinic. Six patients with confirmed primary hyperparathyroidism and hypercalcaemia were studied prospectively. Tc-99m sestamibi gated SPECT was done pre- and postoperatively. The LVEF was abnormally high in all the patients pre-operatively, i.e. above the normal reference range (47-61%) as used in our clinic. It decreased in all of them postoperatively, yet in only three patients to values within the normal range. This was associated with normalisation of the serum Ca(2+) values. The median of the pre-operative LVEF was 74% and postoperative it was 61.5%. The median difference was 9% with a 95% CI for the median difference for paired data (6; 26). This was statistically significant. Increased LVEF was not previously described as part of the clinical picture of primary hyperparathyroidism. The in vivo effect of chronic hypercalcaemia on LV pump function my need to be revisited.