You never know when or where a cardiac emergency will strike, and every second counts.

William Matlock, City of Chattanooga Fire Marshall says, "getting someone started on compression or AED deployed can be the difference between life and death."

That was the case for Christian Bushman about four years ago. What started as a routine day nearly turned tragic.

Christian Bushman says, "I was cleaning my house, and something fell out of the closet and hit me in the chest and put me down. And my husband couldn't get me awake."

So he ran next door to his sister's, who is a certified CPR instructor, house.

Cathy Carson says, "I initiated CPR, had my brother call 911, started doing CPR, did right rate of compressions and got her back."

Emergency crews then arrived, and she was taken to the hospital.

Emergency workers say the average response time during an emergency is 3-5 minutes, which is why the PulsePoint app can make a big difference.

Hamilton County emergency workers joined CHI Memorial and Parkridge Health System to launch PulsePoint, a free mobile app that alerts users when a cardiac event occurs in a public place near their location.

William Matlock says, "if you're [within] a quarter of a mile, they call your phone will alert you there is a cardiac event in progress that gives you the opportunity to act if you wish."

More than 300 thousand people across the country experience cardiac arrest outside of a hospital setting each year, and the American Heart Association estimates less than half received CPR from a bystander in 2016.

Janelle Reilly, of CHI Memorial, says, "that's why it's so important to have as many people in this community download the app, get CPR training and be able to respond as quickly as possible."

Tom Ozburn, Parkridge Health System says, "because we both employ so many healthcare trained people, we provide a workforce that can download the app and become part of the army of heroes."

A victim's chance of survival can double or even triple when CPR is performed until first responders arrive.

Christian Bushman says, "I think it is one of the most important things anybody should learn and especially because they have hands on."

William Matlock says, "the app will also locate additional aid, AED's close to the proximity of where you are."

When you download the PulsePoint respond app, select "Hamilton County Emergency Communications District."

For more information, visit the PulsePoint website.

Here is a list of CPR training resources: