Sudden shock and a new pansystolic murmur at the left lower sternal border days after an anterior (LAD) MI suggests ventricular septal rupture (papillary muscle rupture gives an apical murmur). The immediate test for a suspected mechanical complication is a bedside echocardiogram, which shows the defect/shunt or acute MR and guides emergent surgery. CXR is non-specific, and angiography or right heart catheterisation are not the first immediate test.