Question

20.3 cardiac muscle tissue and the cardiac conduction system
depolarization of cardiac contractile fibers occur because of
slow voltage gated na+ channels opening
slow voltage gated ca++ channels opening
fast voltage gated ca++ channels opening
fast voltage gated na+ channels opening

Explanation:

Depolarization of cardiac contractile fibers is initiated by the opening of fast - voltage gated Na+ channels, which allows a rapid influx of sodium ions into the cell, changing the membrane potential.

Answer:

fast voltage gated Na+ channels opening