A woman shot in the heart during the Las Vegas massacre miraculously survived thanks to the quick-thinking actions of her firefighter boyfriend who rushed her to hospital.

Christina Kitcat was at the open-air Route 91 Harvest country music festival with her boyfriend Kelly Culbertson, who had got them tickets as her birthday present, the Daily Telegraph reports.

The couple initially thought the gunfire was fireworks, but Culbertson soon realised they were caught up in a mass shooting as gunman Stephen Paddock opened fire on music fans from inside room 32135 at the Mandalay Bay Hotel.

"I'm like why did everyone bring fireworks? Why did everybody disperse? Then another round of fireworks goes off, and she looks at me and says, 'It's hard for me to breathe,'" he told the Daily Beast.

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The 27-year-old used all his trauma experience as a firefighter and Emergency Medical Technician to get quickly assess his girlfriend's injuries and get her to safety.

Culbertson, along with two firefighters he had just met, rushed her out of the festival and into a truck heading to hospital with other victims.

He believes that the driver was US Marine veteran Taylor Winston, who stole a pickup truck to carry those seriously injured to hospital.

Ms Kitcat needed open heart surgery after a bullet went through her arm and into a major coronary artery and her lungs.

Shrapnel left four holes in her heart and holes in her lungs, with doctors telling her family it is a "miracle" she is alive.

Mr Culbertson added in the Daily Beast interview: "We have a saying: We prepare for the worst but hope for the best. I hoped to never have seen that. Or experienced it. Or even seen the aftermath of it."

His girlfriend is now recovering in hospital and will celebrate her 30th birthday next week.

Another woman who survived the deadliest shooting in US modern history has penned an emotional thank you note to the strangers who helped save her life.