There is no univocal clinical cardiovascular pattern associated with magnesium deficiency. Only an acute hypomagnesaemia gives the evidence of a real magnesium deficiency. Arrhythmias corrected by magnesium are associated with potassium deficiency. Magnesium deficiency appears to be one risk factor of arrhythmias and coronary spasms. The influence of intravenous magnesium salts was clearly evaluated on cardiovascular electrophysiology allowing protocols infusion. The major beneficial effect of magnesium on total incidence of arrhythmias appears to have been due to a reduction in supraventricular tachyarrhythmias and especially in "torsade de pointes". Antiarrhythmic mechanisms still remain to be clarified. It is likely that magnesium influences cardiac conduction and refractoriness by affecting calcium dependent processes as if acting as an indirect inactivator of slow inward calcium current, probably secondary to an inward shift of the background potassium mediated current. Recent studies demonstrated beneficial effect of intravenous magnesium treatment in acute myocardial infraction, both as to mortality and to early cardiac insufficiency. Beside antiarrhythmic and vasodilatator effects, magnesium seems to show cardiac cells protective action against ischaemia.