Dr. Oz is firing back at Mark Wahlberg's cardiac arrest crack -- and as it turns out, the doc's actually got some jokes of his own ... plus nifty visual aides.
DO took to Instagram Saturday to respond to Mark's own video from a few days ago, where he accepted Oz's no-breakfast/one-legged push-up challenge and then joked the guy would probably need a defibrillator by the time Marky Mark was done with him in the gym.
Well, Dr.