It is well known that magnesium sulfate has a membrane stabilizing effect , and broad spectrum anti arrhythmic properties. In this trial, the investigators study its prophylactic effect against atrial fibrillation in postoperative period of cardiac surgery.

One of the most common postoperative complications after cardiac surgery is postoperative atrial fibrillation (AF). It is rarely fatal but it may cause subjective symptoms and result in thromboembolic complications, heart failure, renal insufficiency, and stroke which may prolong hospital stay.

The risk factors of AF include advanced age, transient atrial ischemia, arterial hypertension, dilated atria, male sex, pulmonary hypertension, previous atrial fibrillation and serum electrolyte disorders . On the other hand, there is evidence that cardiopulmonary bypass (CPB) time, duration of aortic cross clamping and the time of surgery, also the type of cardioplegia and the number of constructed grafts do not influence the incidence of AF.

There are only few studies that show the depletion of electrolytes and serum electrolyte concentration changes after cardiac surgery . The role of potassium in pathogenesis of cardiac arrhythmias is well recognized. Low serum potassium level is often found in association with hypomagnesemia and predisposes to atrial fibrillation. Extracellular magnesium is broadly implicated in neuronal control, neuromuscular transmission, and cardiovascular tone. It has been shown that magnesium suppresses arrhythmias after acute myocardial infarction, and there are studies confirming correlation between hypomagnesemia and postoperative atrial fibrillation . The underlying mechanism of these effects is not well understood but most probably involves magnesium interaction with calcium channels within myocytes membrane. Still the role of magnesium in the pathogenesis of AF is not clear yet.

Also, it is not clear if magnesium supplementation is useful for these patients, or it is useful only in hypomagnesemia patients. Hypophosphatemia and its consequences are less investigated in patients after cardiac surgery. Common complications after cardiac surgery are cardiac and respiratory failure, and they are also among the clinical manifestations of hypophosphatemia. Hypophosphatemia could be the cause of prolonged artificial lung ventilation and myocardial dysfunction; also, it may have influence on the incidence of arrhythmias. Anyway, there are no data confirming the arrhythmogenic effect of changes in serum phosphate level.

Inclusion Criteria:

• Adult patients over 18 years.
• Left ventricular ejection fraction >0.3,
• Blood pressure is normal or less than 180/110.
• ASA ≤ III.
• Normal liver, pulmonary and renal function,
• No diabetes or other metabolism disorders,
• No pulmonary hypertension,
• No atrial fibrillation in the past, sinus rhythm on preoperative electrocardiogram.

Exclusion Criteria:

• history of AF,
• implanted pacemaker,
• postoperative myocardial infarction,
• use of left ventricular assist devices
• Renal failure or on hemodialysis