The symptoms of heart block depend on the type and severity.

First-degree heart block 

First-degree heart block doesn't cause any noticeable symptoms. Most people are only aware they have the condition when they're tested for an unrelated medical condition. It's only recognised by an electrocardiograph (ECG).

Second-degree heart block

Most people with second-degree Mobitz type 1 heart block won't experience any symptoms. However, some people may have symptoms such as:

• light-headedness
• dizziness
• fainting (temporary loss of consciousness)

People with second-degree Mobitz type 2 heart blocks are much more likely to experience the symptoms listed above. They may also have additional symptoms such as:

• chest pain, which may be worse during physical activity, such as climbing the stairs
• shortness of breath 
• tiring easily when doing physical activity
• feeling very dizzy suddenly when standing up from a lying or sitting position; this is caused by having low blood pressure (hypotension)

Congenital third-degree heart block

Many cases of congenital third-degree heart block are diagnosed during pregnancy because an ultrasound scan can often detect whether the baby has a slow heartbeat (bradycardia).

If the diagnosis is overlooked during pregnancy, the symptoms of congenital third-degree heart block won't usually become apparent until the child is older and a greater demand is placed on their heart.

Symptoms of congenital third-degree heart block in older infants or young children include:

• unusually pale and blotchy skin
• lethargy (a lack of energy)
• unwillingness to take part in exercise or physical activity
• dizziness
• fainting

Acquired third-degree heart block

Symptoms of acquired third-degree heart block include:

• light-headedness
• dizziness
• fainting
• fatigue (extreme tiredness)
• chest pain
• slow heart beat (bradycardia)