During right heart catheterization, oxygen saturations are frequently measured from different cardiac chambers in order to identify left to right shunts. If a ventricular septal defect is present, the oxygen saturation will be markedly higher in the right ventricle due to shunting of well oxygenated blood from the left ventricle to the right ventricle. This diagnostic technique can be helpful when a patient presents after an acute MI with pulmonary edema and shock to diagnose an acute ventricular septal defect.