The DefiPace Study

Inclusion Criteria: * Patient is scheduled to undergo elective open chest cardiac surgery (bypass and / or valve surgery) * Patient is at least 18 years old * Patient with isolated bypass surgery is at least 70 years old * Patient with valve surgery is at least 60 years old * Patient provides written informed consent prior to the procedure * Phase B only: patient is scheduled for TMA implantation during the elective cardiac surgery and is potentially eligible for DefiPace use Exclusion Criteria: * Clinical history of either permanent, persistend or paroxysmal atrial fibrillation * Permanent pacemaker/defibrillator, other intra-cardiac active implanted electronic devices * Minimally-invasive surgery * Recent stroke within the last 3 months * A history of or current endocarditis * Pregnacy at the time of surgery