Congestive heart failure (CHF) is becoming more frequent worldwide. Both potassium (K) and magnesium (Mg) deficiencies are common and can be associated with risk factors and complications of heart failure (HF). The major causes of K and Mg depletions are the effects of compensatory neuroendocrine mechanisms (activation of the renin-angiotensin-aldosterone and sympathoadrenergic systems), digoxin therapy, and administration of thiazide or loop diuretic therapy in CHF. Particular attention should be paid to K and Mg restoration in CHF, because of the consequences of both deficiencies (increased arrhythmic risk, vasoconstriction), and the co-supplementation of both ions is necessary in order to achieve K repletion. Mg and K should be employed as first-line therapy in digitalis intoxication and drug-related arrhythmias, and should be considered an important adjuvant therapy in diuretic treated patients with CHF. Another possibility to restore normal K and Mg status is usage of a K, Mg sparing diuretics.