Final answer:
The steep repolarization to rest potential phase of the action potentials of myocardial contractile cells occurs when conductance to K+ ions decrease.
Step-by-step explanation:
The steep repolarization to rest potential phase of the action potentials of myocardial contractile cells occurs when conductance to K+ ions decrease. During repolarization, the K+ channels open, allowing K+ ions to exit the cell. This movement of K+ ions helps bring the membrane potential back to its resting state.