Definition for Isovolumetric relaxation
From Biology Forums Dictionary
As the ventricle begins to relax, the pressure in the ventricle begins to decline. The pressure in the artery (which now has all the ejected blood) is now greater than that in the ventricle. The blood now closes the semi-lunar valve as it tries to go from the artery into the venticle preventing any backflow. Although the pressure in the ventricle is declining, it is still greater than that in the atria so the AV valves are still closed. Thus as the ventricle is relaxing, the volume of blood in the ventricle is not changing. This stage will continue until the ventricular pressure becomes lower than the atrial pressure and the filling stage starts again.
