Final answer:
The typical cardiac action potential shape is rapid depolarization, plateau, and rapid repolarization involving Na+, Ca2+, and K+ ion movements.
Step-by-step explanation:
The typical shape of the cardiac action potential is A) Rapid depolarization, plateau, rapid repolarization. For contractile cells in the heart, the process starts with a rapid influx of Na+, causing a swift rise in the membrane potential that lasts 3-5 ms, leading to depolarization. The membrane potential then plateaus for approximately 175 ms due to the slow influx of Ca2+ ions while few K+ channels are open. The plateau phase is essential as it allows the heart muscle cells to contract fully before another action potential occurs. Finally, the repolarization phase, which lasts about 75 ms, occurs when Ca2+ channels close and more K+ channels open, leading to an efflux of K+, bringing the membrane potential back down to resting levels.