Blood is a constant whereabout in our bodies. As of such a frequent heartbeat exists within our system. Which causes the blood within our bodies to flow forward, in lamense terms it produces a very large push for the blood to distribute it's nutrients throughout the body and back within our heart and out again. This constant push is what prevents blood from flowing backwards in your veins.

No, semilunar valves control the flow of blood out of the heart.

things that could affect the blood flow through the heart

the type of blood vessels which flow contaminated blood to the heart are known as VEINS

The general blood flow path is from the aorta to the heart. The blood will then leave the heart and flow throughout the rest of the body. This path of blood happens every time the heart beats.