Electrolyte disturbances are a common complication of CHF. CHF provides a perfect milieu for the development of these disturbances; renal dysfunction, elevation of neurohormonal substances, activation of the renin-angiotensin-aldosterone axis, and diuretic therapy represent the major contributory factors. Hyponatremia is closely aligned with an unfavorable clinical course. Hypokalemia is associated with increased ventricular dysrhythmias. Hypomagnesemia noted in advanced CHF can be accompanied by arrhythmias and refractory hypokalemia. CHF also offers the ideal milieu (diseased, ischemic, and arrhythmogenic myocardium; elevated catecholamines; and arrhythmogenic drugs) for the threatening clinical consequences (clinical deterioration, dysrhythmias, or death) of these disturbances. These consequences underscore the importance of the recognition, appreciation, and management of these electrolyte abnormalities.