The sinus node is located in the upper part of the right atrium, specifically at the junction of the posterior wall of the right atrium and the entrance of the superior vena cava, under the epicardium. The sinoatrial node is the pacing point for normal sinus rhythm of the heart. It is 20mm long and 2~3mm wide, and is mainly composed of P cells and T cells, of which P cells are pacing cells and T cells are migrating cells. The usual pacing frequency of the sinus node is 60~100 beats/min, and the impulse is conducted to cardiac tissues outside the sinus node through T cells after the formation of P cells. If the sinus node is abnormal, it can cause different arrhythmias, such as sinus tachycardia, sinus bradycardia, sinus arrest, sick sinus node syndrome, and so on. If you are not feeling well, you need to seek medical attention.