Rheumatic fever and rheumatic heart disease continue to be the major health problem in all developing countries including Bangladesh. Rheumatic mitral stenosis is a very common problem in our population having an incidence of 54 percent among rheumatic heart disease with a female preponderance of 2:1. Percutaneous balloon mitral commissurotomy is appealing because the mechanism of valve dilation closely parallels the mechanism of surgical mitral commissurotomy. The technique of balloon mitral commissurotomy has evolved rapidly, with improvements in balloons, guide wires, and the application of double-balloon techniques. There is controversy that whether the presence of AF has a direct negative effect on the immediate or long-term outcome after PTMC in mitral stenosis patients. The purpose of this study was to see the effect of atrial fibrillation (AF) on the immediate clinical and echocardiographic outcome of patients undergoing Percutaneous Transvenous Mitral Commissurotomy (PTMC). The immediate procedural and in-hospital clinical outcome after PTMC of 264 patients with AF were prospectively collected and compared with those of 288 patients in normal sinus rhythm (NSR) with mitral stenosis admitted in National Institute of Cardiovascular Diseases, Dhaka and Al-Helal Heart Institute, Mirpur, Dhaka, Bangladesh. Patients with AF were older than patients with normal sinus rhythm (53 ± 11 vs. 33 ± 12 years; p<0.0001) and presented more frequently with New York Heart Association (NYHA) class III-IV (78.3% vs. 58.5%; p<0.0001), echocardiographic score >8 (38.9% vs. 22.7%; p<0.0001), calcified valves under fluoroscopy (22.2% vs.12.4%, p<0.0001) and with history of previous surgical commissurotomy (21.7% vs. 10.5%; p<0.0001). In patients with AF, PTMC resulted in worse outcomes, as reflected in a smaller post-PTMC mitral valve area (1.6±0.4 vs. 2.1 ± 0.8 cm²; p<0.0001). Patients with atrial fibrillation have a worse immediate clinical and echocardiographic outcome after PTMC.