Twenty-one patients with Double Chambered Right Ventricle [DCRV] associated with Ventricular Septal Defect [VSD] were treated by open heart surgery under cardiopulmonary bypass with moderate hypothermia in the Department of Thoracic and Cardiovascular Surgery, Hanyang University Hospital between June 1982 and October 1984. The following results were obtained 1. The symptoms and physical signs, specific for DCRV, could not be identified. 2. The radiologic findings on simple chest X-ray, specific for DCRV, could not be identified. 3. Electrocardiographic findings, specific for DCRV, could not be identified. 4. Cardiac catheterization was found to be the most important diagnostic method, revealing pressure gradient between proximal chamber and distal chamber in the right ventricle. The average pressure gradient between two chambers showed 48.1523.29 mmHg[varying from 15mmHg to 94mmHg]. 5. Cardiac angiography was found to visualize the anomalous muscle bundles in right ventricle [in 17 cases, 81%] but the evidence of pressure gradient between two chambers within right ventricle is considered necessary for the diagnosis of DCRV. 6. Via surgical observation, anatomical and pathologic findings of the anomalous muscle bundles, associated DCRV were identified. 7. As the direct pressure was measured on the operating table before and after surgery, the average pressure gradient across the muscle bundles showed 40.5219.75mmHg [varying from 16 to 89mmHg] preoperatively and 8.909.72mmHg [varying from 0 to 32mmHg] postoperatively, indicating significant surgical correction of the obstruction present. 8. The presence of anomalous muscle bundles, dividing the right ventricle into two separated chambers, and the presence of the pressure gradient over 15mmHg are considered necessary for the diagnosis of DCRV.