We present an adult with echocardiographic diagnosis of cor triatriatum. Continuous wave Doppler echocardiography was able to assess correctly the severity of the left ventricular inflow obstruction caused by the intra-atrial membrane. Even though the diagnosis was confirmed by catheterization, the surgical decision was based in noninvasive data. Postoperative Doppler echocardiography proved the disappearance of the intra-atrial obstruction. The anatomical information obtained by echocardiography as well as the assessment of the intra-atrial obstruction by cardiac Doppler seem to be sufficient to make surgical decisions in patients suffering from this disease. Both are also suitable to test the result of the surgical intervention.