Late presentation of cor triatriatum with persistent levoatrial cardinal vein.

An asymptomatic 10-year-old boy presented with reduced exercise tolerance and an echocardiographic diagnosis of cor triatriatum. Transthoracic and transesophageal echocardiography failed to reveal the persistent levoatrial cardinal vein discovered at surgery. In patients with late presentation of cor triatriatum with severe mitral inflow obstruction and a small patent foramen ovale, an alternative communication between the posterior collecting chamber and the systemic venous circulation should be sought with alternative imaging techniques.