What is the name of the valve responsible for preventing blood flow from the left ventricle to the left atrium of the heart?

Mitral Valve The mitral valve is a large 'flap' between the two left chambers of the heart. When this is open, it allows oxygenated blood to fill the left ventricle of the heart from the atrium. When the heart contracts or 'pumps' it is closed, so the blood moves out of the left ventricle into the aorta and around the body. If it wasn't closed, there would be back flow of the blood which means there would not be adequate blood flow and oxygenation of tissues.