The purpose of this study is to demonstrate the ability of tedisamil to convert atrial fibrillation or flutter into normal sinus rhythm (NSR) in male patients.

Inclusion Criteria:

• Willing to sign informed consent before screening examinations are performed and before the study drug is administered
• Males > 18 years of age
• Subjects with documented (60 second rhythm strip) symptomatic atrial fibrillation or flutter (duration > 3 hours and < 45 days) at the time of randomization
• Subjects who are in no distress and hemodynamically stable (supine systolic blood pressure > 90 mmHg and diastolic blood pressure < 105 mmHg)

Exclusion Criteria:

• Acute myocardial infarction and cerebrovascular accidents
• Coronary and heart failure symptoms
• Life-threatening ventricular arrhythmias and electrocardiogram (ECG) abnormalities
• Electrolyte abnormalities
• Concurrent antiarrhythmic treatments