Heart attacks are caused by the blood supply to the heart being suddenly interrupted.
Like all other tissues and organs in the body, the heart needs a constant supply of oxygen-rich blood. Without this supply, heart muscles may be damaged and begin to die.
If this is not treated, heart muscles will experience irreversible damage. If a large portion of the heart is damaged in this way, the heart will stop beating (known as a cardiac arrest), resulting in death.
Coronary heart disease (CHD)
Coronary heart disease (CHD) is the leading cause of heart attacks. CHD is a condition in which the coronary arteries (the major blood vessels that supply the heart with blood) get clogged up with deposits of cholesterol. These deposits are called plaques.
During a heart attack, one of the plaques ruptures (bursts), causing a blood clot to develop at the site of the rupture. The clot may then block the blood supply running through the coronary arteries to the heart, triggering a heart attack.
Who's at risk
Risk factors for CHD, many of which are related to each other, are outlined below.
Carbon monoxide (from the smoke) and nicotine both put a strain on the heart by making it work faster. They also increase your risk of blood clots.
Other chemicals in cigarette smoke damage the lining of your coronary arteries, leading to furring of the arteries. If you smoke, you increase your risk of developing heart disease by 24%.
If you eat a diet high in saturated fat, your blood cholesterol levels will rise. This leads to an increase in your risk of CHD and heart attacks. Read more about high cholesterol.
Some foods, such as oily fish, can help lower cholesterol levels. Read our page on preventing a heart attack for more information about how diet can influence your heart attack risk.
High blood pressure
Having poorly controlled high blood pressure (hypertension) can weaken the coronary arteries, making them more vulnerable to CHD. The higher your blood pressure, the greater your risk of CHD and heart attacks.
The increased levels of blood glucose associated with type 1 diabetes and type 2 diabetes can damage the coronary arteries, making them more vulnerable to CHD.
It is estimated that people with diabetes are two to five times more likely to develop CHD than the general population.
Being overweight or obese
Being overweight or obese does not directly increase your risk of CHD and heart attacks, but leads to related risk factors that do. In particular, people who are overweight or obese:
- have an increased risk of developing high blood pressure
- tend to have higher levels of cholesterol as a result of eating a high-fat diet
- have an increased risk of developing type 2 diabetes
Lack of exercise
Lack of exercise is not directly related to an increased risk of CHD and heart attacks. However, it is linked to an increased risk of being overweight or obese and having high blood pressure.
Excessive alcohol consumption can cause high blood pressure and increased blood cholesterol levels, thereby increasing the risk of developing CHD.
Most heavy drinkers tend to have unhealthy lifestyles, such as smoking, eating a high-fat diet and not exercising enough. Read more information about managing your alcohol intake.
Age and sex
The older you get, the more likely you are to develop some degree of CHD.
Men are two to three times more likely to have a heart attack than women.
A number of theories have been suggested to explain this increased risk, such as:
- higher rates of excessive alcohol consumption in men
- more men are overweight than women (although obesity levels are roughly the same for both sexes)
- men may be less effective at coping with stress than women, and increased stress levels may affect their physical wellbeing
- women may be protected by hormones before the menopause
If you have a first-degree relative (a parent, brother or sister) with a history of heart disease – such as angina, heart attack or stroke – you are twice as likely to develop similar problems, compared to the general population.
Rates of high blood pressure and diabetes are higher in people of African and African-Caribbean descent, which means that they also have an increased risk of CHD and heart attacks.
People of South Asian descent (those of Sri Lankan, Indian, Bangladeshi and Pakistani origin) are five times more likely to develop diabetes than the general population. Again, this increases their risk of CHD and heart attacks.
Read more information about health issues for black people and South Asian health.
Research has found that exposure to air pollution – specifically traffic pollution – can cause a significant rise in your chance of developing CHD and, in turn, heart attacks.
Research carried out in 2011 estimated that air pollution could play a part in as many as 1 in 13 cases of heart attacks.
Less common causes
Some less common causes are described below.
Stimulants such as cocaine, amphetamines (speed) and methamphetamines (crystal meth) can cause coronary arteries to narrow, restricting blood supply and triggering a heart attack. Heart attacks from the use of cocaine are one of the most common causes of sudden death in young people.
Lack of oxygen in the blood (hypoxia)
If levels of oxygen in the blood decrease due to carbon monoxide poisoning or a loss of normal lung function, the heart will receive un-oxygenated blood. This will result in the heart muscles being damaged, triggering a heart attack.
An aneurysm is a weakness in a blood vessel wall. If the blood vessel wall becomes weakened beyond a certain point, it will no longer be able to withstand the pressure of blood running through it and will rupture (burst).
Sometimes, an aneurysm can develop inside the coronary arteries, although this is much less common than other types of aneurysm. If a coronary artery aneurysm ruptures, the blood supply to the heart will stop, triggering a heart attack.