The exact rate of the heart rhythm disturbance atrial fibrillation after coronary artery bypass graft surgery is unclear. Atrial fibrillation increases the affected patient’s risk of stroke but also of an earlier death, thus it is important to understand how many patients develop this rhythm disorder, when they develop it and whether it persists. In this study insertable cardiac monitors will be implanted at the time of coronary artery bypass graft surgery to continuously monitor the heart rhythm. With the results we aim to show that more than the assumed ~ 29 % of patients actually develop atrial fibrillation after bypass surgery. A further aim of the study is to investigate the natural history of the rhythm disorder within the first 12 months after surgery.