Beginning of Essay
The heart is bestowed with a specialized system that automatically generates rhythmic control via the sinus node, located in the superior lateral wall of the right atrium near the opening of the superior vena cava. The specialized pacemaker cells dictate control ....

Middle of Essay
.... evolved from simple devices only capable of fixed-rate stimulation of a single chamber of the heart to more sophisticated "implanted computers" that medical personnel can interrogate and reprogram from outside the patient's body. These refinements have allowed for more physiologic pacing with maintenance of atrioventricular synchrony and cardiac output. There are various types of available today that can be surgically implanted to treat specific arryhythmic disorders in the heart. Abnormal rhythms in the heart are one of the most frequent causes of heart malfunction, and in most cases necessitate some type of cardiac pacing unit. Cardiac arrhyt ....