A heart attack (myocardial infarction or MI) is a serious medical emergency in which the supply of blood to the heart is suddenly blocked, usually by a blood clot.
A lack of blood to the heart may seriously damage the heart muscle and can be life-threatening.
Symptoms of a heart attack

Coronary heart disease (CHD) is the leading cause of heart attacks.
CHD is a condition in which the major blood vessels that supply the heart get clogged up with deposits of cholesterol, known as plaques.
Before a heart attack, one of the plaques ruptures (bursts), causing a blood clot to develop at the site of the rupture. The clot may block the supply of blood to the heart, triggering a heart attack.

• Chest pain – the chest can feel like it's being pressed or squeezed by a heavy object, and pain can radiate from the chest to the jaw, neck, arms and back
• Shortness of breath
• Feeling weak and/or lightheaded
• Overwhelming feeling of anxiety
It's important to stress that not everyone experiences severe chest pain; the pain can often be mild and mistaken for indigestion.
It's the combination of symptoms that's important in determining whether a person is having a heart attack, and not the severity of chest pain.

While waiting for an ambulance, it may help to chew and then swallow a tablet of aspirin (ideally 300mg) – as long as the person having a heart attack isn't allergic to aspirin.
The aspirin helps to thin the blood and reduce the risk of a heart attack.
In hospital, treatment for a heart attack depends on how serious it is. The two main treatments are:
• Using medication to dissolve blood clots
• Surgery to help restore blood to the heart

There are five main steps you can take to reduce your risk of having a heart attack (or having another heart attack):
• Smokers should quit smoking
• Lose weight if you're overweight or obese
• Take regular exercise – adults should do at least 150 minutes (2 hours and 30 minutes) of moderate-intensity aerobic activity each week, unless advised otherwise by the doctor in charge of your care
• Eat a low-fat, high-fibre diet, including whole grains and plenty of fresh fruit and vegetables (at least five portions a day)

Complications of a heart attack can be serious and possibly life-threatening. These include:
• arrhythmia – this is an abnormal heartbeat, where the heart begins beating faster and faster, then stops beating (cardiac arrest)
• cardiogenic shock – where the heart's muscles are severely damaged and can no longer contract properly to supply enough blood to maintain many body functions
• heart rupture – where the heart's muscles, walls or valves split apart (rupture)
These complications can occur quickly after a heart attack and are a leading cause of death.
Many people die suddenly from a complication of a heart attack before reaching hospital, or within the first month after a heart attack.
The outlook often depends on:
• Age – serious complications are more likely as you get older
• The severity of the heart attack – how much of the heart's muscle has been damaged during the attack
• How long it took before a person received treatment – treatment for a heart attack should begin as soon as possible