Aim and background: To assess the efficacy and safety of Ibutilide infusion for cardioversion of atrial fibrillation (AF) or flutter (AFL) to sinus rhythm. Materials and methods: This open-label, multicenter phase IV study was conducted at six sites across India. The study enrolled 120 patients (108 with AF, 12 with AFL), each receiving up to two, 10-minute intravenous doses of 1.0 mg Ibutilide. The primary endpoints were the proportion of patients achieving cardioversion and the mean time taken to achieve cardioversion. Secondary endpoints included the proportion of patients maintaining sinus rhythm at 24 hours and the incidence of adverse events. Results: The cardioversion rate at 4 hours post-Ibutilide infusion among 120 patients was 65.83% (n = 79), with an average conversion time of 35.12 ± 36.71 minutes. At 24 hours, 85 patients (70.8%) had successful cardioversion, with a mean time of 107.24 minutes. The majority of patients (71.76%) had achieved cardioversion within 30 minutes. Of the 85 patients who achieved successful conversion, 82 (68.3%) maintained sinus rhythm at 24 hours. A total of 66 patients (55%) achieved cardioversion with the first bolus whereas 19 (15.8%) needed a second bolus. Atrial fibrillation patients had a higher conversion rate (75%) compared to AFL patients (33%). A total of 10 adverse events were recorded in eight patients (6.67%), including nausea, headache, palpitations, and bradycardia. Three severe cardiac events, one case of ventricular tachycardia, and two of tachycardia necessitated discontinuation of Ibutilide. No fatalities or serious adverse events (SAE) were reported. Conclusion: Ibutilide was found to be effective and well-tolerated for rapid restoration of sinus rhythm in patients with AF or AFL. Clinical Trial Registry of India: CTRI/2018/01/011248.