This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Conducting System of Hea, Subject name: Physiology
SA node is the pacemaker, under normal conditions, due to which of the following:- 
Select and explain. 
A. Slow depolarization, slow repolarization, B. Rapid depolarization, rapid repolarization, C. Slow depolarization, early repolarization, D. Rapid depolarization, delayed repolarization
C: Slow depolarization, early repolarization
Answer: C: Slow depolarization, early repolarization 
Explanation: SA node acts as pacemaker because of slow & spontaneous depolarization (due to slow influx of Na (If) causing || in prepotential). Repolarisation is rapid - due to RAPID EFFLUX OF K+ Automaticity is also provided by AV node but recovery after every impulse is fastest in SA node. Every pa of the hea has its own rhythmicity, but they follows the rhythm of SA-node because it has fastest rate and the main reason is Overdrive suppression .