The START-POAF pilot study is a prospective, open-label two-arm, randomized controlled trial with blinded assessment of outcomes (PROBE). This pilot study will assess Atrial Fibrillation (AF) recurrence and burden in patients with new-onset AF following cardiac surgery.

Atrial fibrillation (AF) is the most common abnormal heart rhythm in the world. In patients who have cardiac surgery, new AF is found as an early complication in more than one out of every four surgeries. In the weeks and months after heart surgery, patients who have new AF take a medication called amiodarone to keep their heart in rhythm as it heals. If the heart goes back into AF, patients can have symptoms of heart racing, heart failure (fluid on the lungs) or stroke. Although amiodarone is effective, it can have side effects like dizziness, nausea and slow heart rate. It may also damage the lungs, liver and thyroid gland. Many patients are not able to complete their full prescribed course after surgery. Therefore, it is crucial that the investigators find the shortest possible length of treatment with amiodarone that will keep the heart in rhythm while minimizing the chance of side effects or organ damage. The START-POAF Pilot Randomized Trial will compare two different durations of amiodarone treatment: 1) in-hospital load only and 2) in-hospital load plus 4 weeks after loading dose. All participants will wear an electrocardiogram (ECG) monitor for 4 weeks the day after they complete their loading dose. The investigators will compare the amount of AF seen on the ECG between the two groups.

Inclusion Criteria:

1. Aged ≥18 years;
2. Have undergone cardiac surgery including CABG, valve surgery, ascending aorta replacement, or combinations thereof within 14 days of randomization;
3. Had new-onset POAF (or flutter), documented by 12-lead ECG or lasting ≥ 1 hour on telemetry. Patients can be in AF or sinus rhythm at the time of randomization;
4. Expected to receive 3 g - 5 g of amiodarone loading dose post-surgery.
5. Expected to be ready for hospital discharge within 48 h of randomization.

Exclusion Criteria:

1. Documented preoperative history of paroxysmal, persistent or permanent AF;
2. Planned use of a class I or III anti-arrhythmic drug (other than study drug);
3. Patients who have undergone heart transplant, complex congenital heart surgery, isolated ventricular assist device insertion, or AF ablation (surgical or catheter);
4. Known allergy to ECG adhesives;
5. Contraindication to amiodarone (i.e. hyperthyroidism, severe restrictive or obstructive lung disease, Long QT syndrome, PR > 240 ms, high-grade AV block).
6. Individuals who are pregnant, breastfeeding, or of childbearing potential - female subjects, premenopausal who are not surgically sterile, or, if sexually active not practicing an effective method of birth control (e.g., prescription oral contraceptives, contraceptive injections, intrauterine device, double-barrier method, contraceptive patch, male partner sterilization) before entry and throughout the study; and, for those of childbearing potential, who have a positive pregnancy test at screening