Papillary muscle rupture is a catastrophic mechanical complication of acute MI occurring 2-7 days post-infarction when ischemic necrosis weakens the papillary muscle to the point of partial or complete rupture. The posteromedial papillary muscle is affected 5 times more frequently because it has a single blood supply from the posterior descending artery, whereas the anterolateral papillary muscle has dual supply from both the LAD and circumflex arteries. Complete rupture causes sudden severe mitral regurgitation with massive left atrial volume overload, elevated pulmonary venous pressure causing flash pulmonary edema, and rapid hemodynamic collapse into cardiogenic shock. Without emergent surgical intervention (mitral valve repair or replacement), mortality exceeds 80%.