A myocardial infarction is a heart attack, plainly put. Myocardial refers to the muscle of the heart and infarction refers to a blockage. In most cases of a heart attack, the blockage refers to a blood clot or other entity blocking the blood vessels that supply blood and nutrients the muscles of the heart. When the muscles of the heart cannot get enough blood supply, areas of the heart lack oxygen and begin to die off as a result. A blockage is not the only cause of a heart attack, but we will focus on this particular cause as it is the most common.