This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autonomic nervous system, Subject name: Pharmacology
[{'content': 'The antianginal effect of b-blockers may be attributed to which one of the following \nSelect and explain. \nA. Increased hea rate, B. Increase in diastolic perfusion time, C. Decreased end diastolic ventricular volume, D. Increase in ejection time', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The beneficial effects of b-blocking agents are related to their hemodynamic effects--decreased hea rate, blood pressure, and contractility--which decrease myocardial oxygen requirements at rest and during exercise. Lower hea rate is also associated with an increase in diastolic perfusion time that may increase coronary perfusion. Undesirable effects of b-blocking agents in angina include an increase in end-diastolic volume and an increase in ejection time, both of which tend to increase myocardial oxygen requirement. Ref: Katzung 13e pg:203', 'role': 'assistant'}]