sinus rhythm

sinus rhythm The normal regular rhythm of the heart that is set by the sinoatrial (or sinus) node, which is located in the wall of the right atrium (the right upper chamber of the heart). Normal electrical impulses of the heart start there and are transmitted to the atria and down to the ventricles (the lower chambers of the heart). The lack of normal sinus rhythm is an arrhythmia (abnormal heart rhythm). Sinus arrhythmia refers to the normal increase in heart rate that occurs during inspiration (breathing in). It is a normal response and is more accentuated in children than in adults. See also sinus tachycardia.