NPPB and atrial fibrillation: Secondly, we postulate that postoperative reduction in heart rate and catecholamine-induced tachycardia with ivabradine will correlate with a reduction in biomarkers of cardiovascular stress as measured by NT-proBNP, MR-proANP, MR-proADM and CT-proET-1, which will reduce atrial stretch and postoperative incidence of atrial fibrillation.