The cardiac action potential has five phases. Phase 4 is the resting membrane potential. Phase 0 is the rapid depolarization phase. Phase 1 of the action potential occurs with the inactivation of the fast Na+ channels. Phase 2: This plateau phase of the cardiac action potential is sustained by a balance between inward movement of Ca2+ (ICa) through L-type calcium channels and outward movement of K+ through the slow delayed rectifier potassium channels, IKs. During phase 3 of the action potential, the L-type Ca2+ channels close, while the slow delayed rectifier (IKs) K+ channels are still open.

Click this LINK to visit the original image and attribution information. Right click on the image to save the 800px teaching JPEG.



The cardiac action potential has five phases. Phase 4 is the resting membrane potential. Phase 0 is the rapid depolarization phase. Phase 1 of the action potential occurs with the inactivation of the fast Na+ channels. Phase 2: This plateau phase of the cardiac action potential is sustained by a balance between inward movement of Ca2+ (ICa) through L-type calcium channels and outward movement of K+ through the slow delayed rectifier potassium channels, IKs. During phase 3 of the action potential, the L-type Ca2+ channels close, while the slow delayed rectifier (IKs) K+ channels are still open.