Once Versus Twice Bisoprolol Dosage Regimen in Prevention of Atrial Fibrillation Post Coronary Artery Bypass Graft Surgery

Inclusion Criteria: * Adult patients: 18 to 65 years old * Diagnosed with coronary heart disease or myocardial infarction and scheduled for coronary artery bypass surgery Exclusion Criteria: * History of Ventricular arrhythmia, atrial fibrillation, atrial flutter, left bundle block, AV block grade II/III * History of Sick sinus syndrome, sinoatrial heart block * History of valve replacement * Permanent Pacemaker * LVEF less than 30% * Unstable Heart failure * Cardiogenic shock * Sustained systolic blood pressure less than 100 mmHg or HR less than 50 bpm at recruitment * Severe chronic obstructive airway disease * Severe asthma unless was on previously tolerated bisoprolol dose * Uncontrolled diabetes mellitus unless was on previously tolerated bisoprolol dose * Pregnant/Lactation * Previous recent stroke * Creatinine clearance less than 30 ml/min * End stage liver disease (liver cirrhosis) * Drug dependance history * Untreated phaeochromocytoma * Vasospastic angina * Thyrotoxicosis * History of advanced staged of peripheral vascular disease * Hypersensitivity * Patients on any other beta-blocker other than bisoprolol * Patients on bisoprolol higher than 5 mg/day.