system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Ventricular filling begins at point:
assistant
The correct answer is  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.