Two things make this aortic dissection instead of a heart attack or pulmonary embolism. First, the diastolic murmur is that of aortic insufficiency/regurgitation, which is happening because the dissection is involving the aortic root. Second, the presence of diminished femoral pulses implies that the dissection also involves the descending thoracic aorta distal to the takeoff of the brachiocephalic and left subclavian arteries (which supply the arms). Only an issue in the aorta can cause that constellation of symptoms.