** I'm NOT National CPR Foundation staff ** (Not sure why SiteJabber.com site identifies me as working for NCF).
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While online courses give you theoretical knowledge of CPR & First Aid, these are in-person, HANDS-ON skills that need actual practice. Just as you wouldn't want your massage therapist, physical therapist or surgeon to have ONLY ONLINE training, neither will the person who's life you're trying to save. Why? You won't have the mind-body practice & training to development good judgment on HOW to perform the skills accurately & in the correct places.
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NOTE: CPR done correctly will generally include CRACKING the person's ribs to get enough heart compression. That's how firmly you need to do CPR chest-compressions. Can only learn that thru HANDS-ON practice (e.g. On a CPR-mannequin, like resusci-Annie)