Cardiac Ventricular Muscle Action Potential
Phase	Action	Ion Shifts
0	Rapid Depolarization	Sodium channels open rapidly; inward sodium current drives the membrane potential toward sodium equillibrium at +65mV, but the sodium channels close before this is reached, and the sodium that entered the cell is quickly pumped out
1	Initial Repolarization	Sodium channels are closed, and there is then an outward movement of potassium ions
2	Plateau	Calcium channels open, leading to a slow inward calcium current, balanced by an ongoing outward potassium current
3	Rapid Repolarization	The calcium channels close, but there is continuing outward potassium movement
4	Resting Membrane Potential	Flow across the various potassium channels is re-established at equillibrium

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