Patients (3) presented severe congestive cardiomyopathy of unknown cause. All 3 had a profound depression of serum P levels resulting from the chronic ingestion of large quantities of a P-binding antacid. Results of physical examination and echocardiograms were consistent with cardiomegaly and severe myocardial dysfunction, and chest films showed enlargement of the cardiac silhouette with interstitial pulmonary edema. Serum P was restored to normal levels, and within 2-5 wk the results of physical examination and echocardiogram of each patient returned to normal. These patients had reversible hypophosphatemic cardiomyopathy and show the importance of Pi in myocardial metabolism and function. Serum P measurements should be a part of the routine evaluation of patients with congestive cardiomyopathy because, at least in some patients, hypophosphatemia appears to be a reversible cause of this disorder.