A residual atrial septal defect with bidirectional shunt was detected by transesophageal echocardiography in a 28-year-old man 3 years after percutaneous transluminal mitral commissurotomy (PTMC) with the antegrade transseptal technique. He had had severe mitral stenosis, pulmonary hypertension, and tricuspid regurgitation before the procedure. The result of PTMC was suboptimal, the pulmonary hypertension regressed only partially, and the tricuspid regurgitation remained severe. These factors contributed to the bidirectional shunt. A bidirectional shunt is known to be associated with systemic desaturation and a higher risk of paradoxical embolization and brain abscess. When PTMC is considered in patients with pulmonary hypertension and tricuspid regurgitation, a retrograde left ventricular approach with or without transseptal puncture can avoid the atrial septotomy, decrease the incidence of significant shunt, and should be a rational alternative.