Acute myocardial infarction is the most common cause of cardiogenic shock. Other causes of cardiogenic shock are given in Table 1. The complete occlusion of a coronary artery by a clot causes death of an area of heart muscle that is supplied by that blood vessel and its branches. If a very large area of heart muscle is involved, the general pumping capability of the heart is severely compromised. Because dead myocardium cannot contract, blood cannot be effectively ejected out of the left ventricle into the aorta [see Fig. 1 in the chapter Anatomy of the Heart and Circulation). Blood is held up in the lungs and fluid accumulates in air sacs causing pulmonary edema which results in severe shortness of breath. Because blood cannot be ejected from the heart, the blood pressure falls drastically. When more than 40% of the heart muscle is involved, cardiogenic shock often occurs.