Rare anomalies of atrioventricular connection: hidden or supernumerary valves with imperforate right atrioventricular connection.

We report two hearts with rare anomalies of the atrioventricular connection. Both cases showed muscular partitions within the right ventricle, giving it a double-chambered morphology. In case 1 the floor of the right atrium was muscular, creating the impression of the absent connexion variant of tricuspid atresia. A hypoplastic valve, however, was seen in the right ventricular inlet chamber. Case 2 apparently showed an imperforate Ebstein's anomaly of the tricuspid valve but a supernumerary valve, draining into the left ventricle, was found in a chamber that might correspond to part of the coronary sinus.