Firefighters respond to a variety of calls every day, including (but not limited to): fire-related, medical, MVC, and HazMat. Response statistics from the Toronto Fire Department's 2011 Annual Report show that while fire-related calls have been relatively stagnant over the past seven years, medical calls have increased significantly (Table 1; Figure 1) . Heart disease and stroke account for approximately 350,000 hospitalizations per year in Canada and initial reactions to associated illnesses and symptoms are likely to be common (Heart and Stroke Foundation of Canada, 2014). Myocardial infarction (often called a heart attack) is a common heart condition that firefighters will encounter during their career. This article will discuss myocardial infarctions in more detail than first responders and explore conditions at the senior level of healthcare providers. A myocardial infarction occurs when the blood supply to the heart is limited or stopped due to a blockage in a coronary artery. . Narrowing of the coronary arteries resulting from the buildup of atherosclerotic plaque “causes more than 90% of heart attacks” (Heart and Stroke Foundation of Canada, 2011). As plaque builds up in the arteries, there is an increased risk that it will rupture and cause bleeding which then clots (thrombus). Ischemia (reduction of blood flow to the tissues) of the tissues supplied by the coronary artery is damaged and, with long enough occlusion, dies (American Heart Association, 2012). Signs and Symptoms Most heart attacks begin with mild pain or discomfort in the chest. People who suffer often don't know exactly what is wrong and wait too long to get help (American Heart Association, 2012). It is impera...... middle of paper ......causes occlusion of the vessel and results in greater tissue death. The damage caused by a transmural MI will generally extend much deeper into the muscle tissue (Heuther and McCance, 2012). In cases of myocardial infarction, there is an extreme inflammatory response once the heart begins to repair itself. Necrotic tissue is broken down by enzymes and transported to other parts of the body for elimination (Heuther and McCance, 2012). The scar tissue that initially replaces the necrotic tissue is weak and therefore it will take a few weeks for the patient to feel that they can return to low activity levels. After about six weeks, the necrotic tissue was completely replaced by scar tissue. However, because scar tissue cannot contract and relax like heart muscle does, it will lead to permanent dysfunction (Huether and McCance)., 2012).