I am a paramedic and have witnessed many heart attacks. I can't see this method being of much help.... firstly should the patient breathe and cough
every 2 seconds they would cause themselves to hyperventilate, which will make them feel very lightheaded.
Although you don't have to have any chest pain
to be having a MI (heart attack) if they do then they are going to be in too much pain to breathe deeply!!
Also the heart doesn't always change its rhythm during a MI, if it is a big MI and the rhythm does change then the only thing that is really going to change it back again is high flow oxygen
100%(humans only inhale 21% oxygen no matter how deep they breathe) and drug therapy from the ambulance crew!!