Unless you're experiencing symptoms, heart block is often diagnosed during routine tests for other conditions.

Your GP may suspect heart block based on your medical history, family history and a physical examination.

During a physical examination, your GP may check your pulse and listen to your heart using a stethoscope to check for any abnormal heart rhythms.

They may refer you to a cardiologist (heart specialist) who'll be able to carry out more specialised tests, such as an electrocardiogram (ECG).

Electrocardiogram (ECG)

An electrocardiogram (ECG) measures your heart's electrical activity. It records a trace of the rhythm of your heart and the strength and frequency of the elctrical signals.

An ECG can be carried out while you're exercising (usually on a treadmill or an exercise bike) or while you're resting.

The results can provide a useful overall assessment of how well your heart is working. In some cases it can also indicate whether you have a Mobitz type 1 or Mobitz type 2 heart block.

An ECG is sometimes recorded over a 24-48 hour period because the heart rate can become much slower at various times of the day or night. This is often known as Holter monitoring.

Other tests

Several other tests can be used to diagnose the type and cause of heart block.

First-degree heart block

First-degree heart block doesn't usually require a medical diagnosis. But an exception may be made if it's thought the condition is due to low potassium or magnesium levels. In such circumstances, blood tests may be used to check potassium and magnesium levels.

Second-degree heart block

Blood tests are usually recommended to check whether your heart block is due to an infection, such as diptheria, or high levels of medication, such as a calcium channel blocker. You'll also be referred for an ECG.

Congenital third-degree heart block

Congenital third-degree heart block may be detected during pregnancy using an ultrasound scan. The scanner can measure how quickly your baby’s heart is beating. An abnormally slow heartbeat may signify a heart block.

Congenital third-degree heart block can usually be confirmed before or after birth using an ECG.

Acquired third-degree heart block

Acquired third-degree heart block is usually diagnosed using a combination of blood tests and an ECG. In some cases, an ECG may also be carried out if it's thought that inflammation is affecting the heart muscles.

Due to the often critical nature of third degree heart block, treatment may begin before all blood test results are known.