What Are Some Reasons for a Slow Heart Rate in Humans?

Slow heart rate, clinically known as bradycardia, can result from normal aging, diseases that cause damage to the electrical system of the heart, conditions that slow the heart's electrical impulses and medications used to treat high blood pressure and heart problems, according to WebMD. The normal heart rate in adults is 60 to 100 beats per minute at rest. Heart rates lower than 60 may indicate bradycardia.

Although bradycardia often occurs due to changes in the heart as a person grows older, diseases that inflict damage on the heart's electrical system can also cause the condition, according to WebMD. Heart diseases such as coronary artery disease, heart attack and infections of the heart, including myocarditis and endocarditis, can also cause bradycardia.

In addition, some medical conditions slow the electrical impulses of the heart. These include electrolyte imbalances, which occur when levels of potassium or other nutrients are too high in the blood, or when the person has hypothyroidism. Medications such as beta-blockers, digoxin and antiarrhythmic medications used for the treatment of heart disease and high blood pressure may also cause a lowered heart rate and bradycardia.

A slow heart rate may cause no problems in some people, and may only be a sign that the person is physically fit. However, in other people, the condition may become life threatening and require evaluation by a medical professional.