ABSTRACT
Embolism is the passage of a mass (an embolus) within the bloodstream from a point of origin to a point of impaction. Emboli can be classified conveniently into those arising in the deep veins of the lower limb which pass through the right side of the heart to impact within the pulmonary arterial circulation, and systemic emboli arising mainly within the left ventricle, the left atrium, the valves of the left heart or large arteries which impact within the systemic arterial circulation. Most pulmonary emboli produce no clinical symptoms because they are small and the pulmonary reserve is large. Obstruction of a larger branch of a pulmonary artery tends not to produce an area of ischaemic necrosis (infarction). A high proportion of systemic emboli arise from a mural thrombus secondary to a myocardial infarct. A mural thrombus is attached to the endocardial side of the infarcted heart wall.
