Magnesium ion (Mg) directly inhibits aldosterone production in rat adrenal glomerulosa cells, while potassium ion directly stimulates aldosterone production. It is reported that Mg shows antihypertensive effect in patients with essential hypertension. Secondary hyperaldosteronism induced by diuretic treatment in patients with congestive heart failure accelerates potassium and magnesium ions' excretion in urine. Diuretic-induced falls in potassium and magnesium ions and aldosterone-induced cardiac fibrosis and remodelling are associated with fatal ventricular arrhythmia. Aldosterone antagonists, such as spironolactone and eplerenone, correct not only potassium deficiency but also magnesium deficiency induced by diuretics. Mg supplementation also may be useful procedure to correct potassium and magnesium deficiency, because Mg itself inhibits aldosterone release from the adrenal glands.