Natural pacemaker of heart is:

Ans: d (SA node)Ref: Ganong, 22nd ed Pg. 547SA nodeIt is the natural pacemaker of heart.It is located at the junction of superior vena cava with right atrium.It is made of modified cardiac muscle.Blood supply - by right coronary artery (65%) and left coronary artery (35%).Nerve supply - by Rt vagus and Rt sympathetics.It has the highest rate of impulse generation - 70 to 80 per min.AV nodeIt is located in the right postero inferior region of interatrialseptum near the opening of coronary sinus.lt is made of modified cardiac muscle.Blood supply -by right coronary artery.Nerve supply - by Lt vagus and Lt sympathetic.Rate of impulse generation - 40 to 60 per min.Note: Conduction speed is highest in Purkinjee fibers = 4m/sBundle of His = 1 m/sVentricular muscle = 1 m/sAtrial pathway = 1 m/sSAnode = 0.05 m/sAV node = 0.02 - 0.05 m/s