Opteonâ¢ YF (HFO-1234yf) is a low global warming potential (GWP) refrigerant for use in automotive air-conditioning systems. Opteonâ¢ YF (HFO-1234yf) has a chemical structure of CF3CF= CH2 2,3,3,3-tetrafluoropropene.
During isovolumetric relaxation, which is the second last phase of the cardiac cycle, all the heart valves are closed. This means that there is no blood passing between the cardiac chambers or out of the heart. The pressure drop below 120 mmHg as the ventricles relax causes the semilunar valves to close. As the pressure drops further, the atrial pressure exceeds that of the ventricles and the atrioventricular valves open. Meanwhile, blood is being pumped around the body.
There are also two semilunar valves; one between the right ventricle and the lungs (pulmonary semilunar valve) and one between the left ventricle and the aorta (aortic semilunar valve). The main purpose of the valves is to prevent backflow of blood in the heart. There are things called the chordae tendinae and papillary muscle that help control the opening and closing of the valves as blood flows through them. There are also valves in the veins.