Two cases of congestive heart failure with coexistent magnesium and potassium depletion are described. The prolonged QTc intervals and ventricular premature beats of the first patient and the idionodal tachycardia of the second patient disappeared only after magnesium repletion, which normalized both extra- and intracellular potassium and magnesium levels. The third patient had a case of urosepsis while on total parenteral nutrition. He developed diarrhea, hypocalcemia, hypokalemia, hypomagnesemia, weakness, muscular fasciculations and athetoid movements. The neurological manifestations were relieved and the biochemical abnormalities normalized only after magnesium repletion.