Sinoatrial (SA) node
Nodus sinuatrialis
CardiovascularOrgansThorax
- What it is
- A small crescent of specialised pacemaker cells in the wall of the right atrium where the superior vena cava enters, at the top of the crista terminalis.
- Function
- Fires spontaneously 60–100 times a minute, starting every normal heartbeat (sinus rhythm).
- Size
- About 10–20 mm long, 3–5 mm wide, ~1 mm deep under the epicardium.
- Clinical note
- Supplied by the SA-nodal artery (from the right coronary artery in ~60% of people); its rate is sped up by sympathetic nerves and slowed by the vagus.