Until relatively recently, it was generally believed that hypomagnesemia was a rare entity in clinical practice. It is clear, however, from newer studies that the overall incidence of hypomagnesemia in hospitalized patients can range from 7 to 52%. The greatest association of hypomagnesemia in hospitalized patients appears to be in hypokalemic states and in patients confined to intensive care units. Most of these patients demonstrate cardiovascular abnormalities, ranging from cardiac arrhythmias and atrial fibrillation to hypertension. On the basis of primarily epidemiologic and experimental findings, it has been suggested that there may be a strong association between the dietary intake of Mg (and errors in the Mg metabolism and distribution of Mg in the body), the concentration of this element in the myocardium and blood vessels, and the risk for development of cardiac arrhythmias, sudden death ischemic heart disease, hypertension, transient ischemic attacks, strokes and pre-eclampsia-eclampsia. During the past 5-6 years, a considerable amount of new, quantitative clinical evidence has been found which lends considerable support to these tenets. Clinical trials utilizing Mg as a therapeutic tool to treat refractory arrhythmias, digitalis toxicity-associated arrhythmias, myocardial infarctions, diabetic angiopathy, transient ischemic attacks, cerebral resuscitation, hypertension and 'classical' migraine are under way, and to an extent have been successful. Careful assessment of serum, blood cells, and urine for free versus bound Mg should be done routinely in cardiovascular disease and high-risk patients.