Cardiac Action Potential Phases — All Points Reach Plateau, Restore

Expansion

• A — All → Phase 0: rapid depolarisation (Na⁺ channels open; membrane shoots to +30 mV)
• P — Points → Phase 1: early partial repolarisation (transient K⁺ outflow)
• R — Reach → Phase 2: plateau (Ca²⁺ influx balances K⁺ efflux; unique to cardiac muscle)
• P — Plateau → Phase 3: rapid repolarisation (K⁺ channels dominate; Ca²⁺ channels close)
• R — Restore → Phase 4: resting membrane potential restored (Na⁺/K⁺ ATPase activity)