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
Parasympathetic stimulation of heart causes: 
Select and explain. 
A. SA node decreases firing, B. Increased AV node excitability, C. Decreased ventricular contraction, D. Tachycardia
A: SA node decreases firing
Answer: A: SA node decreases firing 
Explanation: None