Sharply depolarizes
The resting membrane potential of cardiocytes is -90mV and it can reach up to +20mV during depolarization. The action potential of cardiocytes are divided into phases: Rapid depolarization, Plateau, Rapid repolarization. Plateau is unique in cardiomyocytes.
There 3 ion channels that is needed for cardiac action potential. These are the fast, voltage gated sodium channel, variable potassium channel, slow calcium channel