The tendons you are talking about are called the cordae tendineae not heart strings
These tendons are anchored to the wall of the ventricle by chordae tendinease, which prevent the valve from inverting. The chordae tendinae are attached to papillary muscles that cause tension to better hold the valve.
The tendons of the valves in the heart, such as the chordae tendineae, help to anchor the valve flaps (or cusps) and prevent them from being pushed back into the atria during ventricular contractions. This helps to ensure that the valves close properly and prevent backflow of blood.
The chordae tendineae, also known as the heart strings, are fibrous tendons that anchor the heart valves in place and prevent them from turning inside out during the cardiac cycle. These tendons are connected to the papillary muscles in the heart to ensure proper valve function.
The atrioventricular valves are held in place by the chordea tendeae. These tendons are chord like structures that stiffen to close the valve.
tendons
tendons
Tendons attach muscle to bone.
Tendons attach muscles to bones.
Tendons are attached to muscles.
Tendons do flex.
The left atrioventricular valve stops the back-flow of blood by only being opened if a large force or pressure is behind it (in the left atrium) and is closed if a large force or pressure is in front of it (in the left ventricle).