Between the superior vena cava and the right atrium of the heart, the automatically conducting organ or sino-atrium node (SAN) is called the pacemaker. SAN or SA Node is the natural pacemaker. Aging, congenital heart disease, heart attack, open heart surgery, etc. can cause the natural pacemaker to become damaged or unusable. An artificial or mechanical pacemaker is used when the natural pacemaker is damaged. Irregular heartbeat is called arrhythmia. American scientists William Chardack and Wilson Greatbatch (1969) invented the implantable pacemaker.