The heart's electrical signals start in the heart's "pacemaker," a specific node of cells. Located in the upper right atrium, the crescent-shaped pacemaker measures about half an inch (13.5 ...

When the patient's heart was removed, a portion of the right atrium was left behind including the native sinoatrial node (SA node). A new heart was implanted which also included a SA node.

Sinus arrhythmia is an abnormal heart rhythm that starts at the sinus node. Find out about the symptoms, types, and outlook for sinus arrhythmia. Medical News Today ...