All diseases that damage the heart muscle such as heart attack, cardiomyopathy, myocarditis and hypertension, can also damage the electrical system of the heart. But there are also diseases that seem to affect only the electrical system and not the other structures. They also exist as isolated juvenile or congenital pathologies but are very rare. Sometimes simply due to the aging of the cardiac electrical system. The consequences on the heart can be mild and such as not to significantly compromise its frequency and rhythm, or they can be serious to the point of causing dangerous slowing of the heart rate or even interruptions of cardiac activity. Thus, for example, if the compromise of the electrical activity consists of a slowing of its frequency, this will not generally cause unpleasant sensations, it may, at most, cause fatigue. If, on the other hand, the electrical damage causes the interruption, even temporary, of the heart's activity we could have sudden dizziness or loss of consciousness or, in the most serious cases, cardiac arrest.

Damage to the electrical system can occur at different levels. It can be localized damage to the source of the impulses (sinus node) or to the wires that conduct the impulse (conduction system). If the sinus node stops working properly, the heart rate may accelerate or slow down. If the heart rate is too high or too low, the chambers of the heart do not contract as they should and are unable to supply the correct amount of blood to the body. There may also be problems with the path that the impulse follows as it passes from the upper to the lower part of the heart. Thus, the impulses, which start in the right atrium, may arrive at the ventricles with a significant delay or may not reach them at all. This condition is called “atrioventricular block”. This block can occur at different levels: the atrioventricular node, the bundle of His or the right and left bundle branches. If the impulse does not reach the ventricles, they have a certain reserve mechanism, but the beats generated by the ventricles alone are too slow and too weak. Heart block can also cause a loss of normal synchrony between the atria and ventricles. This condition consists of incorrect timing of contractions between the atria and ventricles or between the right and left ventricles. The consequence is that the ventricles cannot fill as much as they should and cannot pump the blood that the body requires.

These are the most common reasons that require the implantation of a pacemaker.

Often the electrocardiogram is not able to establish the location of the electrical damage and sometimes it is not even able to see if there is any damage, for which the doctor may prescribe specific tests, for example a continuous 24-hour electrocardiogram (Holter) or the recording of the heart's electrical signals directly from the inside using appropriate catheters (electrophysiological study).