A heart attack, medically known as a myocardial infarction, occurs when the blood flow that brings oxygen to the heart muscle is severely reduced or cut off completely. This happens because the coronary arteries that supply the heart with blood can slowly become narrow from a buildup of fat, cholesterol, and other substances, known as plaque. When a plaque in a heart artery breaks, a blood clot forms around the plaque. This blood clot can block the blood flow through the heart muscle.

There are several types of heart attacks, characterized by their severity and the specific damage they cause to the heart muscle:

1. ST-Elevation Myocardial Infarction (STEMI): This is the most serious type of heart attack. It occurs when a coronary artery is completely blocked, leading to a large portion of the heart muscle being unable to receive blood. It is characterized by a specific pattern on an electrocardiogram (ECG).
2. Non-ST-Elevation Myocardial Infarction (NSTEMI): This type of heart attack occurs when the blood supply to a part of the heart is severely reduced or cut off, but not completely. It's usually less damaging than a STEMI but still requires immediate medical attention.
3. Coronary Artery Spasm: Also known as Prinzmetal's angina, this rare type involves a temporary spasm in a coronary artery. It can block blood flow to the heart muscle temporarily and cause symptoms similar to a heart attack.
4. Silent Myocardial Infarction: This refers to a heart attack that does not have the typical symptoms. It may go unnoticed or be mistaken for something else.

Risk factors that can lead to a heart attack include high blood pressure, high cholesterol, smoking, obesity, sedentary lifestyle, poor diet, diabetes, and family history of heart disease. Lifestyle changes and medical treatment can help manage these risk factors.