We describe a 70-year-old woman who underwent successful percutaneous Inoue antegrade-technique mitral valvuloplasty. Three months later, the patient developed right-sided heart failure. Color Doppler echocardiography and cardiac catheterization demonstrated an atrial septal defect with bidirectional shunting and no restenosis of the mitral valve (iatrogenic Lutembacher's syndrome). Percutaneous treatment was successfully accomplished using a 13 mm Amplatzer Septal Occluder (AGA Medical Corporation, Golden Valley, Minnesota). The causes of right-to-left shunting and the effects of body position on gas exchange in such patients are also discussed.