The CPR mouth-to-mouth "kiss" wakes David up, like how the kiss Charming gave Snow White during her sleeping curse woke her up.
For the part where Mary Margaret revives David, Ginnifer Goodwin was taught CPR by a medic, but it "looked bad". Jennifer Morrison then taught her how they did it on the latter's old television series House because CPR is more dramatic on-screen.
Footage from Snow White and Prince Charming's scenes were re-used in the Season Three finale Snow Drifts (2014) and There's No Place Like Home (2014), which combines old footage and reshoots.