An abnormal heart rhythm is a change in either the speed or the pattern of the heartbeat — the heart may beat too slowly, too rapidly or irregularly. When the heart beats too slowly, too little blood is pumped out to the rest of the body. When the heart beats too quickly, it cannot fill completely so the body doesn't receive the blood volume it needs to function properly. Slow heart rates are called bradycardias. Fast heart rates are called tachycardias.
The heart is made up of four chambers. The upper chambers, called the atriums, receive and collect blood. The lower chambers, called the ventricles, pump blood to the body. Working together, the chambers of the heart move life-sustaining blood throughout the body.
There are several types of abnormal heart rhythms, some occur in one of the atriums and are called atrial, others occur in the ventricles and are called ventricular.
Reviewed by health care specialists at UCSF Medical Center.