This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiac Cycle, Subject name: Physiology
"Incisura" of the aerial pulse corresponds to: 
Select and explain. 
A. First hea sound, B. Closure of the aoic valve, C. Isovolumetric relaxation, D. Third hea sound
B: Closure of the aoic valve
Answer: B: Closure of the aoic valve 
Explanation: Incisura is the notch seen in the aerial pulse tracing due to closure of the aoic valve. More peripheral aerial pulsations exhibit an analogous notch called "dicrotic notch". At the end of ventricular systole, there is sudden change in the direction of blood ('protodiastole'), followed by closure of the aoic valve. These events are responsible for the notch, a sudden alteration in the aerial tracing. It is followed by a slowly declining pressure wave, indicating the ventricular diastole.