This study is a multicenter, randomized, subject and Investigator-blinded, placebo-controlled, parallel-group, multiple ascending dose-ranging study to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) effects of MAA868 in patients with atrial fibrillation (AF) or flutter at low risk of thromboembolic stroke or peripheral embolism.

Inclusion Criteria:

• Male and female patients ≥ 18 and < 85 years old with paroxysmal atrial fibrillation (PAF) or atrial flutter on 12 lead electrocardiography at Screening Or
• Patients with a history of PAF or atrial flutter, as documented by (telemetry, 12 lead electrocardiography or ambulatory [e.g. Holter] monitor) and not due to a reversible condition (e.g. alcohol binge drinking) can be entered even if they do not have PAF at Screening. There is not time-limit for this.
• Patients with a Congestive heart failure, Hypertension, Age ( > 65 = 1 point, > 75 = 2 points), Diabetes, previous Stroke/transient ischemic attack (2 points) (CHA2DS2-VASc) risk score (tool as a predictor for estimating the risk of stroke in patients with atrial fibrillation (AF); Lip et al 2010) of 0-1 for men and 1-2 for women and in whom, in the investigator's judgment, the use of an anticoagulant for stroke prevention is not indicated

Exclusion Criteria:

• History of stroke, transient ischemic attack or systemic embolism
• History of major bleeding during treatment with an anticoagulant or antiplatelet therapy. (Patients who have had major bleeding on anticoagulants or antiplatelet therapy more than a year ago can be enrolled only if the bleeding was due to a reversible cause, e.g. gastro-duodenal ulcer that was successfully treated.)
• History of traumatic or non-traumatic intracranial, intraspinal or intraocular bleeding
• Known bleeding diathesis or any known active bleeding site at screening or baseline
• Family history of bleeding disorder
• Known active GI lesions predisposing to bleeding events
• Myocardial infarction, unstable angina pectoris or coronary artery bypass graft (CABG) surgery within 12 months prior to the Screening period
• Known clinically significant valvular heart disease including moderate or severe mitral stenosis (valve area <1.5 cm2)
• Patients with a prosthetic heart valve

Other protocol defined Inclusion/Exclusion criteria may apply

Adverse event information was collected at every study visit from providing written informed consent for participation in the study (on Days -28 to -3) until Day 170 (the end of study visit).

The occurrence of adverse events was to be sought by non-directive questioning of the participants at each visit by the site staff during the study (e.g., "How are you feeling today?" or "How have you been feeling since your last visit") to elicit adverse event information from the participant. Adverse events might have been detected when they were volunteered by the participants during or between visits or through physical examination finding, laboratory test finding, or other assessments.