For the purposes of the story it's a "vaccination against death", keeping an unconscious person in cardiac arrest alive. But why are they unconscious in the first place? Because the brain ran out of oxygen! If it worked, you would be awake and mobile through asystole. Cardiac arrest would be a medical emergency-- solved by the patient getting in a car and driving to the ER. (Maybe not a good idea, though: the big locomotor muscles would run out of oxygen first, so you'd probably lose the ability to steer or press the brake pedal halfway there...)

Even more boring of a nitpick: if the molecule provided oxygen without binding to the resulting CO2, then loss of blood flow would result in rapid carbolic acid buildup and ischemic injury from pH imbalance. You'd die from metabolic acidosis before you would die from lack of oxygen. The "respirocyte" artificial blood cell concept from 1998 had two internal tanks for that purpose, one metering out O2 and one collecting CO2: https://www.tandfonline.com/doi/pdf/10.3109/1073119980911768...