More than 200 defibrillators have been installed at O2 stores across the UK.
The life-saving devices have been registered on the British Heart Foundation's National Defibrillator Network, which will allow 999 call handlers to quickly direct people to their nearest device in an emergency.
Virgin Media O2 has also provided more than 800 employees with online sessions or in-person training in CPR.
Brenda Edwards, whose family has experienced heart conditions and cardiac arrest, praised the campaign.
She called on the public to learn life-saving skills, including CPR.
"I think there are so many people who are nervous and scared of what [CPR] might be," she told Sky News. "I basically want to say don't be scared, don't be nervous about it. It literally takes 15 minutes to do this training and it is so clear and concise.
"And most importantly, it helps to save lives."
Talking the public through how to use one of the new defibrillators, she said: "Well, basically, when I went to the O2 store, there was the defibrillator in the case.
"You open the case, you push the power on and the defibrillator machine starts talking to you literally step by step. You cannot put a foot wrong because it is that easy.
"Over 800 staff have been trained in this as well to help out. On the British Heart Foundation website, you can access the training for free as well.
"It sounds daunting because it is a life and that is a scary prospect. But once you have done this training like myself and gone through it, it is that easy."
She said her brother had collapsed on the high street in Bristol and his heart had stopped for 20 minutes, but "fortunately for him" there was a passer-by who knew how to administer CPR.
"But with these defibrillators, if anybody finds himself in that situation, in that case of emergency, they can contact the medical responder who will be able to tell you which O2-owned store the defibrillator can be found in," she added.
"Every second counts. I'm hoping that more companies will want to catch up to this so that you could have a defibrillator in every store."