Despite the crucial role of calcium in myocardial contractility, hypocalcemia has been rarely reported as a cause of heart failure. In this article, the authors describe a case of severe hypocalcemia caused by idiopathic hypoparathyroidism and worsened by concomitant hypomagnesemia. The patient presented with congestive heart failure that improved dramatically with amelioration of plasma calcium levels. This case and other similar cases in the literature revealed that hypocalcemic heart failure is reversible. Measurement of plasma calcium should be included in the initial work-up of all patients with heart failure, and plasma magnesium must also be checked and corrected if hypocalcemia is demonstrated. (c)2001 CHF, Inc.