Atrial fibrillation

- Participant must be 18 to 85 years of age inclusive, at the time of signing the informed consent.
- Participant is hemodynamically stable and does not require emergency cardioversion, as determined by the investigator.
- Participant has a current episode of atrial fibrillation (AF) ongoing for at least 3 hours and no more than 30 days at the time of randomization.
- Participant has an indication for electrical cardioversion of AF, as determined by the investigator according to standard clinical practice and national/institutional guidelines.
- At randomization, successful initiation and achievement of therapeutic levels of anticoagulation therapy, as well as completion of imaging evaluation for left atrial thrombi, as appropriate for the duration of the AF episode and risk for the participant according to national guideline and institution-specific routine practice.
- BMI within range [18 – 39.9] kg/m2. 
- Contraceptive use by participants or participant partners should be consistent with the study protocol and local regulations regarding the methods of contraception for those participating in clinical studies.
- Signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol
- Willing and able to comply with the receipt, home use, and return of the continuous ECG recording device, as well as with the participation in scheduled telephone follow-up assessments.

- Current atrial flutter (AFL) or combined AF/AFL
- Contraindication for electrical cardioversion on planned treatment day
- Documented severely dilated left atrium (left atrial diameter, LAD >5 cm) measured by any modality within the 6 months prior to screening; if several values are available, the most recent one shall be reported. If left atrium diameter was not measured in the last 6 months or a major cardiovascular event occurred within the last 6 months, a new measurement must be done at screening
- Unsuccessful conversion of current AF episode (pharmacologically or electrically)
- Known severe valvular heart disease (e.g., severe mitral regurgitation, severe aortic stenosis)
- Patients with NYHA Class ≥ III heart failure, or with active management of acute heart failure decompensation on treatment day.
- History within the preceding 3 months prior to randomization of any of the following events, or any other significant cardiovascular event as judged by the investigator:
 -- Stroke
 -- Myocardial infarction
 -- Unstable angina pectoris or other signs of myocardial ischemia
 -- Cardiac surgery
 -- Transcatheter valve replacement
 -- Percutaneous coronary intervention (PCI)
 -- Coronary artery bypass graft (CABG) or other revascularization procedure
- Severe renal impairment, i.e., estimated glomerular filtration rate (eGFR) <30 mL/min/1.73m² (using CKD-EPI formula) or requiring dialysis
- Severe hepatic impairment, i.e. Child Pugh Class C
- Use of anti-arrhythmic class I or III drugs within 5 half-lives before study drug administration (oral amiodarone in the previous 3 months)
- Hypertension with SBP ≥ 180 mmHg or hypotension (SBP < 90 mmHg) at randomization (based on the second BP measurement)
- Stressor-associated AF, i.e., in the setting of an acute and reversible stressor (e.g., cardiac surgery, myocarditis, endocarditis, sepsis, pneumonia, etc.). This includes ablation procedure within the preceding one month prior to randomization.