Heart block can be present from birth (congenital) or develop later in life (acquired).

Babies are more likely to have congenital heart block if they're born with a heart defect, or if their mother has an autoimmune condition, such as lupus.

Acquired heart block

Acquired heart block can affect people of any ages, but older people are more at risk.

There are several causes, including:

• heart surgery – thought to be one of the most common causes of complete heart block
• being an athlete – some athletes get first-degree heart block because their hearts are often bigger than normal, which can slightly disrupt their heart's electrical signals
• a history of coronary heart disease, heart attack or heart failure – this can leave the heart tissues damaged
• some diseases – such as myocarditis, cardiomyopathy, Lyme disease, sarcoidosis, Lev's disease, diphtheria or rheumatic fever
• exposure to some toxic substances
• low levels of potassium (hypokalaemia) or low magnesium (hypomagnesemia) in the blood
• high blood pressure (hypertension) that isn't well controlled
• cancer that's spread from another part of the body to the heart

• a penetrating trauma to the chest – such as a stab wound or gunshot wound

   Certain medications can also cause first-degree heart block, including:

• medication for abnormal heart rhythms – such as disopyramide

• medications for high blood pressure – such as beta blockers, calcium channel blockers, or clonidine
• digoxin – a medication used to treat heart failure
• fingolimod – used for treating certain types of multiple sclerosis 
• pentamidine – used to treat some types of pneumonia
• tricyclic antidepressants  – such as amitriptyline