Abstract We have studied 21 patients who had lifethreatening congestive heart failure refractory to standard anticongestive measures. The condition of 1 patient was unresponsive both to ethacrynic acid and to meralluride, and this patient was the only one whose condition was refractory to ethacrynic acid irrespective of dosage. Two patients had greater initial responses to large doses of meralluride than to relatively small doses of ethacrynic acid, but larger doses of ethacrynic acid evoked responses equal to those of meralluride. In 5 patients, large doses of meralluride and initial doses of ethacrynic acid were equally potent. In the largest group, of 13 patients, ethacrynic acid was far more potent than meralluride, although in some of these patients hypokalemia and digitalis intoxication were induced by ethacrynic acid. After ethacrynic acid therapy, reversal of dilutional hyponatremia was a dramatic response in some of the patients.