Slowest conduction is seen in the following pa of the cardiac conducting system:

Depolarization initiated in the SA node spreads radially through the atria, then converges on the AV node. Atrial depolarization is complete in about 0.1 s. Because conduction in the AV node is slow, a delay of about 0.1 s (AV nodal delay) occurs before excitation spreads to the ventricles. This delay is shoened by stimulation of the sympathetic nerves to the hea and lengthened by stimulation of the vagi. From the top of the septum, the wave of depolarization spreads in the rapidly conducting Purkinje fibers to all pas of the ventricles in 0.08-0.1 s. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 29. Origin of the Heabeat & the Electrical Activity of the Hea. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.