A Study to Investigate the Efficacy, Safety, Tolerability and Pharmacokinetics of PKN605 in Participants With Atrial Fibrillation

Inclusion Criteria:

• Inclusions at Screening

• Signed informed consent must be obtained prior to participation in the study

• Male and female participants ≥ 18 years of age

• History of at least 2 episodes of AF

• At least 1 of the AF episodes specified in inclusion #3 must be within the last 12 months (or during screening) and documented by 12-lead ECG, Holter, or anyother ECG recording method, as confirmed by the Investigator

• One or more of the following:

• AFB of 1% or higher on a local ambulatory Holter, mobile cardiac telemetry, ECGpatch monitor, or other ambulatory electrocardiographic monitor within the last 12months

• CHA2DS2-VASc score of 2 or higher in males, 3 or higher in females (1 point forcongestive heart failure, hypertension, age 65-74 years, diabetes, vascular disease,female sex; 2 points for age 75 years or older, prior stroke or transient ischemicattack)

• Stable heart failure or with New York Heart Association class I or II symptoms

• NT-proBNP level of 300 pg/mL or higher on a local lab test within the last 12 months

• On guideline-directed stroke prevention treatment, as confirmed by theInvestigator

• Participants must have a body mass index (BMI) ≥ 18 kg/m2. BMI is calculated asbody weight (kg) divided by height (m) squared

• Inclusions at Day 1

• Sinus rhythm at Baseline documented by 12-lead ECG (participants withpersistent AF should be cardioverted at least 12 hours before randomization)

Exclusion Criteria:

-Exclusions at Screening

• Permanent AF

• Ongoing reversible causes of AF (e.g., hyperthyroidism, myocarditis, acute alcohol,sepsis- or infection related AF, surgery-related AF, pulmonary embolism)

• Ongoing use of antiarrhythmic therapy (Vaughan Williams class I or IIIanti-arrhythmic therapy must be discontinued at least 7 days before Screening phaseECG patch monitor; amiodarone must be discontinued at least 6 weeks before Screeningphase ECG patch monitor)

• History of an AF ablation procedure within the last 6 months without a recurrence ofAF at least 2 or more months after the ablation.

• Implanted pacemaker, defibrillator, or cardiac monitor

• Infiltrative (e.g., amyloidosis, sarcoidosis) or hypertrophic cardiomyopathy

• Left ventricular ejection fraction of 40% or less documented within the last 12months, or during Screening

• Current decompensated heart failure or hospitalization for heart failure within 3months prior to Screening