A Heart Attack, medically called a myocardial infarction, occurs when blood flow supplying part of the heart muscle becomes sufficiently reduced or blocked that cardiac muscle cells are deprived of oxygen and begin to suffer injury and die. Most heart attacks result from disruption of an atherosclerotic plaque within a coronary artery followed by formation of a blood clot that obstructs blood flow.
The term does not mean that the heart has necessarily stopped beating; cardiac arrest is a different emergency in which the heart can no longer maintain effective circulation. The amount of permanent damage depends on which coronary vessel is affected, the location and duration of obstruction, the availability of alternative blood flow and how rapidly treatment restores circulation.
The classic mechanism involves atherosclerosis, in which fatty material, inflammatory cells and fibrous tissue accumulate within the walls of coronary arteries. A vulnerable plaque can rupture or erode, exposing substances that activate platelets and the clotting system. A thrombus can then enlarge rapidly and obstruct the artery. Heart attacks are classified partly according to their electrocardiographic and pathological characteristics, including ST-elevation myocardial infarction and non-ST-elevation myocardial infarction. Another clinically important distinction is between myocardial infarction caused by an acute coronary blockage and myocardial injury from other causes, such as severe anaemia, prolonged rapid heart rate or profound physiological stress.
Symptoms vary considerably. Central or left-sided chest pressure, squeezing, heaviness or discomfort is characteristic, but pain may radiate to the arm, shoulder, back, neck or jaw. Breathlessness, sweating, nausea, vomiting, dizziness and unusual weakness can occur. Some people, particularly older adults and people with diabetes, may have few typical symptoms or predominantly experience breathlessness or fatigue. Symptoms can also be mistaken for indigestion or other conditions. Because heart-muscle damage increases with prolonged interruption of blood flow, suspected myocardial infarction requires urgent emergency medical assessment rather than waiting to see whether symptoms disappear.
Diagnosis generally combines the clinical presentation with electrocardiography and blood testing for cardiac biomarkers, particularly cardiac troponins. Troponin is released when myocardial cells are injured, and serial measurements can help establish whether injury is acute. An ECG can identify characteristic electrical changes and can guide immediate treatment, although a single normal ECG does not necessarily exclude myocardial infarction. Additional investigations may include echocardiography, coronary angiography and imaging selected according to the clinical circumstances. Clinicians also consider alternative explanations for chest pain and myocardial injury because an elevated troponin is evidence of heart-muscle injury rather than, by itself, proof of a particular cause.
Emergency treatment aims to restore coronary blood flow, limit further myocardial injury and prevent complications. Depending on the type and circumstances, treatment can include antiplatelet medicines, anticoagulant treatment, medicines that reduce cardiac workload and urgent coronary revascularisation. Percutaneous coronary intervention can mechanically open an obstructed coronary artery, usually using a catheter-based procedure and often a stent. Thrombolytic medicines may be considered in particular circumstances when timely catheter-based reperfusion is unavailable. Treatment decisions depend on ECG findings, timing, bleeding risk, anatomy, coexisting disease and local protocols.
Complications can include dangerous arrhythmias, heart failure, cardiogenic shock, recurrent infarction, inflammation around the heart and mechanical damage to cardiac structures. The extent and location of muscle damage influence ventricular pumping function and therefore subsequent risk. Some complications occur immediately, while others can emerge during recovery. After an infarction, scar tissue forms as damaged myocardium heals; scar does not contract normally and can contribute to impaired ventricular function or create a substrate for certain arrhythmias. Prompt reperfusion is consequently important not only for immediate survival but also for preservation of long-term cardiac function.
Recovery involves secondary prevention and cardiac rehabilitation as well as treatment of the acute event. Depending on the individual, long-term management may include antiplatelet therapy, lipid-lowering treatment, blood-pressure control and medicines that reduce subsequent cardiovascular risk. Stopping smoking, maintaining appropriate physical activity, addressing diet and managing diabetes and other risk factors can reduce the likelihood of further events. Cardiac rehabilitation provides supervised exercise, education and risk-factor management and can also address confidence and return to everyday activities. Medication adherence is particularly important because many preventive treatments reduce future cardiovascular events even when the person feels completely well.
A Heart Attack is best understood as an acute manifestation of coronary artery disease rather than simply as "chest pain" or "a blocked heart". Risk is influenced by factors including age, smoking, high blood pressure, abnormal cholesterol, diabetes, obesity, family history and other vascular conditions, although an infarction can occur in people without an obvious risk profile. Women can experience different or less typical symptom patterns, and younger adults can also be affected. The distinction between myocardial infarction, angina, heart failure and cardiac arrest is clinically important: they can coexist, but they describe different processes. Persistent or severe symptoms suggestive of a heart attack warrant immediate emergency medical attention.
