While the EMS crew is rushing in, they say it's important someone is already tending to the patient suffering the heart episode.
The friend, family member or stranger's efforts could be the difference of life or death.
"It's already not a very high chance of survival when you go into cardiac arrest," explained MMR Paramedic Supervisor, Josh Fox. "When you don't do any compressions or CPR, the body's not circulating anything at all."
Fox said that causes damage to your organs and your brain. So he said it's critical to start the CPR as soon as the person's pulse ends and don't stop.
"You find the tip of the breast bone. Once you locate that, place the heel down, two hands, make sure you get up hard and fast two inches, at least a hundred times a minute," he explained.
Simple steps Fox said will stick with you even in the chaos of someone unexpectedly passing out.
"Try to do the best you can for as long as you can if no one else is there to help you. Because any CPR is going to be better than none," Fox said.
And even when the emergency crews arrive, Fox said don't immediately stop. Any interruption to the chest compression's can be detrimental.
"We'll walk in and everyone will just back up and now nothing's happening; and, we're still trying to figure out what's going on. So, if you could just stay on the chest, if you're able to, until someone tells you not to," he said.
Because you're pushing hard and fast so close to the person's sternum, Fox explained you could break it; but, he said, that's an indication you're doing CPR properly.
"You might see a change in the skin color from being blue because they weren't breathing, heart wasn't beating. They might change a little bit, for the better," he said.