My veterinarian used intracardiac injection to euthanize my cat. Did the cat feel any pain?

The American Veterinary Medical Association (AVMA) Guidelines for the Euthanasia of Animals: 2013 Edition state that intracardiac injections are acceptable when performed on anesthetized or unconscious animals.  The intracardiac injection procedure is unacceptable when performed on awake animals, due in part to the high probability of pain.