The exact cause of atrial fibrillation is unknown, but it's more common with age and affects certain groups of people more than others.
Atrial fibrillation is common in people with other heart conditions, such as:
It's also associated with other medical conditions, including:
But not everyone with atrial fibrillation has one of the conditions above. It can sometimes affect people who are physically very fit, such as athletes.
When no other conditions are associated with atrial fibrillation, it's known as lone atrial fibrillation.
Certain situations can trigger an episode of atrial fibrillation, including: