# How do we regulate our heartbeats? **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2011, 9:28pm UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058 "2011-07-14T21:28:20Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![George\_Kaplin](https://avatars.discourse-cdn.com/v4/letter/g/3e96dc/32.png) [@George\_Kaplin](https://boards.straightdope.com/u/George_Kaplin)\ **Post date:** [July 14, 2011, 9:28pm UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058/1 "2011-07-14T21:28:20Z")
I was just wondering, how does our body know how often to make our hearts beat? I get that there’s some sort of organic pacemaker in place, but how does the pacemaker know how many beats the heart needs to make per minute to keep us conscious? ---
**Author:** ![HamishBlake](https://avatars.discourse-cdn.com/v4/letter/h/50afbb/32.png) [@HamishBlake](https://boards.straightdope.com/u/HamishBlake)\ **Post date:** [July 14, 2011, 9:34pm UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058/2 "2011-07-14T21:34:11Z")
The Sinoatrial Node is the body’s natural pacemaker > **[Sinoatrial node](https://en.wikipedia.org/wiki/Sinoatrial_node)** > > The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximately 15 mm long, 3 mm wide, and 1 mm thick, located directly below and to the side of the superior vena cava. > These cells can produce an electrical impulse known as a cardiac action potential that travels through the electrical conduction system of the he... ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 14, 2011, 9:40pm UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058/3 "2011-07-14T21:40:13Z")
The “organic pacemaker” as you call it is a group of specialized cells called the sinoatrial node or SA node. The SA node normally would fire at a fairly high rate, something like 100 to 115 beats per minute. The SA node also gets a signal from the vagus nerve to slow it down though, and the end result is a resting beat of around 60 to 80 beats per minute. When you exercise, the signal from the vagus nerve is reduced, and the heart speeds up. It’s actually a bit more complicated than that, because other tissues can generate the firing trigger if the SA node isn’t working properly, but that’s the basic idea of it. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 14, 2011, 11:05pm UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058/4 "2011-07-14T23:05:21Z")
OK, so that’s a partial answer - the next question is: How does the Sinus node change the pulse rate in response to exertion? ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 15, 2011, 1:14am UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058/5 "2011-07-15T01:14:07Z")
When you exercise, sensors in your aorta and carotid arteries detect a higher level of carbon dioxide in the blood and send this signal to your brain. Your brain then increases your heart rate by reducing the signals on the vagus nerves (in other words, your brain doesn’t tell the heart to speed up, the brain tells the heart to beat less slowly). There is also another nerve signal from the brain (whose name I can’t remember) that tells the SA node to beat faster and with more force. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [July 15, 2011, 1:57am UTC](https://boards.straightdope.com/t/how-do-we-regulate-our-heartbeats/589058/6 "2011-07-15T01:57:22Z")
It’s not just exercise that affects the heartbeat. I have aortic stenosis, meaning the valve between my heart and aorta is constricted, and becoming more so in time. At some point, possibly soon, I will need a new valve. But meanwhile, the heart “knows” that it needs to work a little harder to get the blood flowing properly. Otherwise I’d be passing out, or worse. Unfortunately, the heart can only do so much, before the surgery becomes imperative. But meanwhile it’s truly amazing that the heart “knows” it needs to pump more blood.