The purpose of this study is to investigate non-linear heart rate variability indexes as predictors of the incidence of cardiac arrhythmias in patients undergoing cardiac surgery, including coronary artery bypass graft (CABG) and valvular surgery.

Inclusion Criteria:

• All patients who will have cardiac surgery
• The patient must be mentally able and willing to participate in the study
• Male or female patients over the age of 18

Exclusion Criteria:

• Patients with major renal, hepatic, respiratory, or cerebral dysfunction
• Patients with atrial fibrillation or other forms of sinus node dysfunction
• Patients requiring continuous artificial pacing
• Patients with significant congenital heart disease with or without arrhythmias
• Patients on Intra-Aortic Balloon Pump
• Patients experiencing cardiac emergencies or undergoing cardiac salvage operations