@herstein.jacob what was the decision on this? new card?
Don’t remember this discussion and don’t have access to UW Step 1 anymore…
I keep forgetting haha. @Stillmatic can you check? Is a new card warranted?
The resting membrane potential of cardiac cells is primarily determined by potassium (K+) ions. These cells have a higher permeability to potassium ions due to the presence of potassium channels, which allows potassium to flow out of the cell more easily, leading to a negative resting membrane potential.
Anyway as far as uworld goes:
Resting membrane potential and action potential
The action potential results from changes in the membrane permeability to K+ and Na+ ions. Depolarization results from massive influx of Na+ through voltage-gated Na+ channels. Repolarization occurs due to closure of voltagegated Na+ channels and opening of voltage-gated K+ channels. K+ ion permeance is highest during the repolarization phase of the action potential. 
Changes in membrane potential occur in response to changes in neuronal membrane permeability to various cellular ions. The more permeable the membrane becomes for a cellular ion, the more that ion’s equilibrium potential contributes to the total membrane potential.