Cardiac action potentials pacemaker

What is the primary characteristic of Phase 4 in the pacemaker cardiac action potential, and how does it contribute to the heart's rhythmic activity?

1: Rapid depolarization due to a large influx of Na + ions, leading to heart contraction.
2: Slow, spontaneous depolarization due to the funny current, contributing to automaticity.
3: Stabilization of membrane potential, preventing heart rate fluctuations.
4: Rapid repolarization due to outward K + currents, resetting the heart rhythm.