Why does a heart beat twice?

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When listening to a heartbeat it consists of two thumps. Is it contracting twice very quickly or is the second thump caused by something else?

In: Biology
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It beats twice because the heart pushes blood through 2 chambers. I beat per chamber essentially.

A heart “beat” is actually a few processes happening at once. The first process is the top part of the heart (atria) contracting to fill the bottom part (ventricles). The top part squeezes blood through the tricuspid and mitral valves into their respective ventricles. These valves close and the second stage begins. The ventricles begin squeezing and then the aortic and pulmonic valves open allowing blood to exit. These valves close and the process begins again.

Your heart consists of two parts–the atria and the ventricles. The ventricles are the part that does all the actual contraction to push blood to your lungs (on the right side) or to the rest of the body (on the left side. There’s entry valves, which open inwards and close when the pressure in the ventricles get high; and exit valves, which open outwards and close when the pressure in the ventricles gets low.

The first sound (called “lub” in medicine…yes, really) is the sound of the “entry” valves to the ventricles slapping shut as the main contraction happens. The second sound (“dub”) is the sound of the “exit” valves snapping shut as the muscle relaxes and the heart starts to fill.

[This](https://www.youtube.com/watch?v=A2YoGyNhAns) is a nice animation.

~~The first thump (“Lub”) is the heart pulling blood in to exchange gases. The second thump (“Dupp” or “Dub”) is the heart pushing blood out after oxygen is replenished by the lungs.~~

“Lub” is the sound of one set of valves opening, and “dub” is the sound of the other set of valves opening.

EDIT: I have been corrected, and I apologize.

There are two beats, the first squeezes the blood from the atria to into the ventricles, the next squeezes the ventricles to force the blood throughout the body.

The atria serve as holding tanks for the ventricles ensuring that blood can continue to flow into them throughout the cycle, and then prime the ventricles to ensure they’re full before their cycle

The ventricles are the high pressure pumps which actually do the work of sending the blood around your body. If you just had ventricles your blood would have to stop flowing briefly as once the system is pressurized it wouldn’t have anywhere to go until the ventricle begins refilling, but in our system the atria expand to give the blood somewhere to flow to.

Those sounds are the sounds of valves closing. Basically, you have to upper chambers, and two lower chambers. The top two squeeze first, then the bottom two. Their valves snap shut closely together, making two distinct heart sounds. You can sometimes hear them more individually. It’s not the heart beating twice; it’s different parts of the heart making their sounds through the progression of the heart beat.