i think you mean bypass
Your heart keeps your blood "flowing"
a flap of tissue that prevants blood from flowing backward is
If blood starts flowing backwards through a valve, stroke volume and ejection fraction would decrease. The heart's pumping action would be less efficient.
valves in the veins
heart valves
your skin of course!
These are called valves.
Valves in the veins prevent the blood from flowing backward or from pooling.
The heart valves keep blood from flowing backward. This increases the efficiency of the pumping of the heart.
a valve
Heart valve.
The four heart valves.