Closing  of  the  mitral  valve  begins  at point:
At point D, the pressure within the left ventricle is less than the pressure in the left atrium, and, therefore, the mitral valve opens and ventricular ﬁlling begins. At point A, the ventricle begins to contract, raising its pressure above that in the atrium and closing the mitral valve. The aortic valve opens at point B and closes at point C.
A
B
C
D