Patients randomized to the rhythm monitoring arm will assess their heart rhythm with a photoplethismography (PPG) based smartphone application (FibriCheck™). Measurements are performed three times daily and while experiencing symptoms. The patients start measuring immediately after discharge and continues until the scheduled postoperative consultation with the cardiologist or cardiac surgeon at 21-91days after discharge.

Patients randomized to the rhythm monitoring arm will be discharged without protocol mandated rhythm monitoring. A postoperative consultation is scheduled with the cardiologist or cardiac surgeon at 21-91days after discharge.

Heart Rhythm assessment using the FibriCheck™ application with the patient's proprietary smartphone, three times daily, from discharge until follow-up consultation (day 21-91 after discharge).

Any of the following therapeutic interventions:

• Initiation or unplanned continuation of anticoagulation drug therapy resulting from arrhythmia detection
• Initiation or increase in dose regimen of anti-arrhythmic drug therapy (Vaughan-williams class 1 or 3)
• Cardioversion
• Cardiac implantable electronic device (CIED) implantation

Prespecified postoperative adverse events:

1.1. Acute respiratory insufficiency 1.2. Pleural effusion 1.3. Pneumonia 1.4. Pulmonary Embolism 1.5. Pneumothorax 1.6. Atelectasis, leading to respiratory insufficiency

2.1. Acute myocardial infarction 2.2. Symptomatic arrhythmia 2.3. Pericardial effusion 2.4. Pericarditis 2.5. Endocarditis 2.6. Systemic embolism 2.7. Cardiogenic shock

3.1. Acute stoke including cerebrovascular accident (CVA) and transient ischemic attack (TIA)

4.1. Renal failure, defined as: >50% increase in serum creatinine or initiation of renal replacement therapy 4.2. Urinary tract infection, requiring antibiotic treatment

5. Wound related complications requiring surgical intervention or antibiotic treatment.

6. Sepsis

7. Other unplanned hospitalisations will be classified by the research team as 'postoperative adverse event' or 'unrelated to the cardiac surgery procedure'. Such events will be reported with the study results.