Abnormal heart rhythms; Bradycardia; Tachycardia; Fibrillation

An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm. The heart can beat too fast (tachycardia), too slow (bradycardia), or irregularly.

An arrhythmia can be harmless, a sign of other heart problems, or an immediate danger to your health.

Heart, section through the middle

The interior of the heart is composed of valves, chambers, and associated vessels.

Heart, front view

The external structures of the heart include the ventricles, atria, arteries and veins. Arteries carry blood away from the heart while veins carry blood into the heart. The vessels colored blue indicate the transport of blood with relatively low content of oxygen and high content of carbon dioxide. The vessels colored red indicate the transport of blood with relatively high content of oxygen and low content of carbon dioxide.

Normal heart rhythm

An electrocardiogram (ECG) test measures the electrical activity of the heart. A normal resting heart rate is 60 to 100 beats per minute.


Bradycardia heart rhythms are characterized by a slowness of the heartbeat, usually at a rate under 60 beats per minute (normal resting rate is 60 to 100 beats per minute).

Ventricular tachycardia

Ventricular tachycardia is a rapid resting heart rate initiated within the ventricles, typically at 160 to 240 beats per minute (normal resting rate is 60 to 100 beats per minute).

Atrioventricular block,  ECG tracing

This picture shows an ECG (electrocardiogram, EKG) of a person with an abnormal rhythm (arrhythmia) called an atrioventricular (AV) block. P waves show that the top of the heart received electrical activity. Each P wave is usually followed by the tall (QRS) waves. QRS waves reflect the electrical activity that causes the heart to contract. When a P wave is present and not followed by a QRS wave (and heart contraction), there is an atrioventricular block, and a very slow pulse (bradycardia).

Conduction system of the heart

The intrinsic conduction system sets the basic rhythm of the beating heart by generating impulses which stimulate the heart to contract.



Exams and Tests


Outlook (Prognosis)

When to Contact a Medical Professional