Ventricular septal rupture (VSR) is a catastrophic mechanical complication of acute myocardial infarction, occurring in 1-2% of cases, typically 3-5 days post-MI when the infarcted myocardium undergoes coagulative necrosis and becomes weakest. The rupture creates a communication between the left and right ventricles, causing acute left-to-right shunting of oxygenated blood across the defect. The magnitude of shunting depends on the defect size and the ratio of pulmonary to systemic vascular resistance; large defects cause massive left-to-right shunting, volume overloading both ventricles (the right ventricle receives its normal venous return plus the shunted blood), producing biventricular failure, pulmonary edema, and cardiogenic shock. Clinical presentation includes sudden hemodynamic deterioration, a new loud holosystolic murmur with palpable thrill at the left sternal border, and progressive shock. Differentiation from acute mitral regurgitation (from papillary muscle rupture) is critical: VSR produces a step-up in oxygen saturation from the right atrium to the pulmonary artery on right heart catheterization. The nurse recognizes sudden deterioration in a post-MI patient, identifies the new murmur, initiates hemodynamic monitoring, manages afterload reduction to decrease left-to-right shunting, assists with intra-aortic balloon...