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.
The left ventricle pumps blood through the aortic semilunar valve into the aorta. From the aorta, blood enters into systemic circulation throughout the body tissues until it returns to the heart via the vena cava and the cycle repeats. The semilunar valve on the left side of the heart is the aortic valve, named for the fact that it prevents the aorta from regurgitating blood back into the left ventricle. 2  The semilunar valves are smaller than the AV valves and do not have chordae tendineae to hold them in place.