1. It is not appropriate to attempt resuscitation of an elderly dog that has a history of heart failure. A heart (be it human or canine can only be brought out of ventricular fibrillation by an electric defibrillator).
2. Assuming that a dog has suffered an acute trauma and was otherwise relatively healthy until the incident that has rendered them unconscious this is the protocol advised:
Open the airway by extending the head into a natural position and pulling the tongue out (this will remove any obstruction in the airway, extreme caution should be taken if you attempt to remove any obstruction yourself) Observe for breathing for 10 seconds, use a hand resting on the chest (do not use your cheek against the nose as recovery can involve an involuntary bite)
If there is no breathing give 3-5 breaths to the nose (pulling the tongue out will prevent air going into the stomach), looking down to the chest to observe the rise of the chest and stop each breath when you see the chest rise.
Reach between the back legs to locate a pulse or use the capillary refill test on the gums to determine if there is a circulation. If you are uncertain, assume that there is no circulation (as there soon won’t be if the canine is no longer breathing). Turn the canine onto their right side (as long as this is possible) and give 15 compressions at a rate of 100-120 bpm to an area mid chest, behind the “elbow”. Aim to give compressions to a 1/3 of the depth of the chest.
Repeat 3-5 breaths followed by 15 compressions until signs of life return or you are too tired to continue.
Beware of any sign of recovery as the canine may well vomit or bite in fear (even if they are very familiar with you).
Immediately transport to a vet or continue to treat if bleeding is a concern.