This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart: Rhythmical Excitation of the Heart, Subject name: Physiology
Which of the following causes increase in conduction velocity of impulse through heart - 
Select and explain. 
A. Vagal stimulation, B. Parasympathetic stimulation, C. Sympathetic stimulation, D. All of the above
C: Sympathetic stimulation
Answer: C: Sympathetic stimulation 
Explanation: Ans. is 'c' i.e., Sympathetic stimulation o Effects of sympathetic stimulation are :Heart positive chronotropic (| heart ratef ii) Positive ionotropic (| contractility), iii) Positive dromotropic (| conduction velocity), iv) Positive bathmotropic (increased automaticity), v) Decreased refractory period in all cardiac cells.Vasoconstriction | total peripheral resistance (due to arteriolar constriction), |venous capacitance (due to venoconstriction)Increased stroke volume, cardiac output and BP.o Effects of parasympathetic stimulation areNegative chronotropic (decreased heart rate) : - Vagal stimulation cause decrease in slope (flattening) of prepotential (pacemaker potential) and therefore the time taken to reach the threshold levelis increased - Heart rate is decreased.Negative dromotropic (decreased conduction).Increased refractory period of all type of cardiac cells.