A Myocardial Infarction (more commonly known as a heart attack), is the hearts response to a decreased or sometimes complete lack of blood flow to the myocardium, this results in loss in function of cardiac muscle and consequently a lower cardiac output that can potentially lead to complete cardiac arrest. 
The most common cause of myocardial infarction is pre existing Coronary heart disease (CHD), this is a disease that is caused by lack of blood flow through the coronary arteries (the arteries that supply the myocardium with blood). There are many contributing factors to CHD, although many are lifestyle related, those with poor diets, low level of physical activity, family history, or those who smoke, excessively drink alcohol, or abuse drugsb are at a much higher risk of developping CHD.
- ↑ http://www.nhs.uk/Conditions/Heart-attack/Pages/Introduction.aspx NHS Choices
- ↑ http://www.nhlbi.nih.gov/health/health-topics/topics/heartattack/causes.html What Causes a Heart Attack, National Heart,Lung and Blood Institute, [Accessed 2013]