What is happening during the plateau phase of
cardiacdepolarization?
A) Sodium ions block voltage-gated calcium ion channels.
B) Acetylcholine is hyperpolarizing the SA node
C) Nothing - all ion gates and valves are closed.
D) voltage-gated potassium ion channels open to allowpotassium
ions to diffuse out.
E) Calcium ions enter the cystol of cardiac myofibers
fromsarcoplasmic reticulum and through voltage-gated
slowchannels.

Heart contains the cardiac myocetes cells that are surrounded by the sarcolemma. Heart has the ability to conduct the electrical impulse same as the muscle cell have.

The plateau phase is the second phase of the cardiac action potential. During this phase, the calcium ions moves out of the cell from the sarcoplasmic reticulum to the cytosol through voltage gated sodium calcium channels. Sodium ions will move inside the cell during this phase.

Thus, the correct answer is option (3).