The valves of the ventricles in the heart are held in place by chord-like structures called "Chordae Tendinae". They ensure that during the contractions of the heart, the valves remain tightly shut, so as to prevent mixing of oxygenated and deoxygenated blood.
The Bicuspid, Tricuspid, Aortic Semilunar, and Pulmonary Semilunar valves of the heart are connective tissue sheaths which allow for the flow of blood in one direction. The valves‘ structure, resembling a ballooning connective tissue pocket, tolerate the increasingly high pressures of the atria and ventricles by ballooning outwards as blood fills. String-like structures known as Chordae Tendinae attach along the edges of the valves and run towards point of attachments on the respective atrium/ventricle. It is important to note that these structures do not actually pull open the valves. Valves in the heart instead open when the pressure in the heart, generated by the contractile tissue of the heart, exceeds a certain threshold at which the valves are essentially blown open. The chordae tendinae thus help stabilize the valves when they are opened due to the high pressure.
Your heart is a muscle and it contracts (squeezes) to move blood. The heart can be divided into a top half (atria) and bottom half (ventricles). Listen to your heart beat or someone else's heart beat. You can hear two parts to each beat: lub-dub, lub-dub, lub-dub.
Those sounds are the sounds of the valves in the heart shutting.
There are four primary valves in the heart which can be divided into two categories: the atrioventricular valves and the semilunar valves. The "lub" is the sound of the atrioventricular valves. The "dub" is the sound of the semilunar valves.
The atrioventricular valves connect the atria (atrio-) to the venticles (-ventricular). There are two atrioventricular valves, the tricuspid and bicuspid, one for each side of the heart. These valves open when the atria squeeze the blood down to the ventricles. The pressure pushes the valves open and the blood drops into the bottom half of the heart, the ventricles.
The ventricles are much stronger than the atria. So strong, in fact, that they would push the blood back up the wrong way if there was nothing to stop them. The atrioventricular valves are kept closed by the chordae tendinae. You may have heard the phrase, "Tug on my heart strings." The chordae are your heart strings. They pull tight on the valves to keep them shut when the ventricle is beating.
The tricuspid valve connect the right atrium to the right ventricle. (Hint: You should always TRI- to be RIGHT). It gets its name from the fact that it has three (tri-) cusps. Each one of these cusps is connected to the chordae to pull it closed.
The bicuspid, sometimes also called the mitral valve, connects the left atrium to the left ventricle. It has two cusps, which are connected to the chordae. The reason it is sometimes called the mitral valve? Bishops wear a hat with two leafs on it called a mitre that looks very similar to the valve!
Interestingly, you can "break your heart strings" or rupture your chordae. If this happens, the blood will go the wrong way when the ventricles beat! This is called "regurgitation" and can cause health problems.
The other two valves of the heart are semilunar valve, the aortic and pulmonic valve. These valves don't have cusps or chordae. Instead, these valves look like half moons (semi- -lunar). They also open when the pressure of blood is powerful enough to push them open. These valves also shut on their own when the pressure relaxes. However, they don't need special chordae to keep them shut!
In short:
- The pressure from the heart pumping the blood opens the valves.
- The valves shut when the heart relaxes.
- The chordae are thick ropes which hold the atrioventricular valves shut.
Further reading:
http://www.innerbody.com/image_card02/musc31-new.html#continued
The heart is a muscular structure whose purpose is to pump blood through the body. The heart valves serve to direct the flow of blood in one direction, and they are made of sheets of connective tissue called leaflets, which as a flap. The valves open and close due to differences in pressure, so when the pressure behind them is greater than the pressure in front, the valves open and blood flows in. When pressure is greater in the other direction, the valves shut so as to prevent blood from flowing in the wrong direction. There are a number of different valves connecting the four chambers of the the heart, and which valves are open or closed depends on the contraction of the left and right ventricles. When the ventricles contract and blood is pushed through, there are tendinous structures called the chordae tendinae that help pull the atria-ventricular flaps close, like strings pulling a lid shut.
https://www.fi.edu/heart/structure-heart
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