Valves - thin membranes found mostly in veins to prevent blood (flowing at relatively low pressures) from flowing backwards.
They are called valves
There are atrioventricular valves on each side of the heart that keep blood from flowing from the ventricles back up into the atria. There are also semilunar valves that prevent blood from flowing from the pulmonary arteries and aorta back into the right and left ventricles, respectively.
These are valves, and are found in veins to prevent blood from flowing backwards.
valves help prevent blood from flowing in the wrong direction by opening and closing at the right time to let the heart pump blood effectively.
valves
They stop blood flowing the wrong way. If blood tries to go the wrong way for whatever reason, they automatically seal shut and prevent blood flow until the blood is flowing properly again.
There are two ways that blood is kept flowing in the same direction. The heart is pumping it in that direction, and blood vessels contain valves which prevent blood from flowing in the wrong direction.
Valves.
the semi lunar valves stop the blood flowing the wrong way !
There are valves in the blood vessels (like a one-way door) - that stop the blood flowing backwards.
valves
One directional valves keep blood in the heart flowing in the right direction. There are three valves: biscupid valve, semilunar valve and tricuspid valve. These open to let the blood flow through then close to prevent the blood flowing back in the wrong direction making the heart less efficient.