Transthoracic and transoesophageal echocardiography (TTE, TEE) were performed in 130 consecutive patients referred for mitral balloon valvotomy. Atrial septal aneurysms were diagnosed by TTE and TEE in 2 and 3 patients, respectively. All 3 patients underwent mitral balloon valvotomy via the transseptal route. The foramen ovale was found to be patent in 2 of these patients, thus rendering puncture of the interatrial septum unnecessary. In the 3rd patient transseptal catheterisation was performed through the wall of the aneurysm itself. There were no significant complications in any of these patients. No left-to-right interatrial shunting could be demonstrated by oximetry in any of the 3 patients. Transoesophageal colour flow imaging showed trivial shunting in 2 patients and none in the 3rd. Transseptal mitral balloon valvotomy can be performed safely in patients with atrial septal aneurysms, especially in those with co-existent patent foramen ovale.