As Cor Triatriatum is a rare congenital cardiopathy and benign after corrective surgery, decisive means of diagnosis are essential. The AA review some descriptive theoretical concepts and make reference to the difficulties, present at times, in diagnosis by cardiac catheterization. They consider Eco-Doppler to be the means of excellence for its recognition describing all aspects that point to the diagnosis of this pathology. Described is the case of a 12 month old baby, in whom some semiological findings had lead to a wrong diagnosis. In the discussion, additional diagnosis is eliminated due to some anatomic characteristics defined by echocardiography.