This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Which of the following physiological change can occur when there is vagal stimulation of hea? \nSelect and explain. \nA. Increased R-R interval, B. Increased hea rate, C. Increased cardiac output, D. Increased force of contraction', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Stimulation of parasympathetic (vagus) fibers causes decrease in the hea rate (increased R-R interval), reduce the force of contraction, and constrict the coronary aeries. Stimulation of sympathetic nerves increases hea rate (decreased RR interval). Ref: Moon D.A., Foreman K.B., Albeine K.H. (2011). Chapter 4. Hea. In D.A. Moon, K.B. Foreman, K.H. Albeine (Eds), The Big Picture: Gross Anatomy.', 'role': 'assistant'}]