At rest, your heart normally beats between 60 and 80 times a minute. A rate lower than 60 beats per minute (bradycardia) is normal only if you are resting, asleep, or very physically fit.

There are two causes of abnormally slow heart rate:
the SA node may fire too slowly, or the electrical signal cannot propagate normally from the atria to the ventricles.

An abnormally slow heart rate or a very long pause between beats can cause tiredness, lightheadedness, or fainting. This condition is treated with a pacemaker.

Tachyarrhythmia

Exercise, mental or emotional stress, and some illnesses can cause your heart rate to accelerate. A heart rate over 100 beats per minute is called tachycardia. A tachycardia can be a normal adaptation to certain conditions (for example exercise) or, can occur inappropriately, and is then called a tachyarrhythmia.

 
Warning: This information should not be used as a substitute to consultation from a physician.

The contraction of the heart muscle is triggered by an automatic electrical impulse. The impulse is caused by a specialized group of cells located in the right atrium. When the electrical impulse or the conduction pathways, which transmit the impulse across the cardiac muscle are disrupted, the heart rate is either slowed, accelerated, or the rhythm becomes irregular.

 
This can cause disturbances such as fainting, light-headedness or fatigue. Various tests are often performed, which you may have already undergone, such as electrocardiogram (ECG), 24-hour continuous ECG recording (Holter), and heart rhythm studies via temporary catheters placed inside the heart (electrophysiological test). Depending on the severity of the signs or symptoms, and the outcome of the tests, the implantation of a pacemaker may be recommended.