Rupture of an aneurysm of the aortic sinus of Valsalva into the right ventricle is described. Surgery revealed a small aneurysm ruptured into the right ventricle near the tricuspid valve without aneurysmal involvement of the tricuspid valve. The cineangiogram revealed a shunt from the aortic sinus into the right atrium not during systole but during diastole, and increased oxygen saturation was found in the right atrium. The unusual hemodynamics in this case was most probably due to the closure of the small aneurysmal opening due to myocardial contraction during systole, so that the shunt flow through the aneursymal tract occurred only during diastole and was directed toward the right atrium due to the location of the aneurysm. Thus, even without aneurysmal involvement of the tricuspid valve or tricuspid regurgitation, the oxygen saturation increased in the right atrium.