According to the Fresno Fire Department, crews respond to more calls about heat exhaustion, drowning and cardiac arrest when temperatures rise.
Action News asked some firefighters how likely is it someone is already performing CPR when they arrive - they said around 30%.
"Knowing how to do CPR can make an incredible difference in a person's life," said Jonathan Lopez, Fresno Fire public information officer.
Lopez added that CPR increases a person's chance of survival.
"Up to two and three times what it would normally be if they didn't get CPR or even an AED application," he said.
The American Heart Association reports 70% of cardiac arrest episodes occur at home. The CDC reports more than 60% of drownings happen in a home pool.
This is why Fresno Fire wants the public to know how to do CPR because it can save a loved one.
Hands-only CPR includes opening the victim's airway and performing chest compressions.
"Lock your hands together and keep your arms straight, and then you're going to push hard and fast, at a rate of 100 beats per minute," explained Lopez.
Firefighters said there could be sounds of popping or cracking.
"That means you're doing it right," Lopez said.
Fire crews also understand some might be scared to do CPR because they don't want to hurt the victim, or possibly be sued.
"There are what are called 'Good Samaritan Laws' that protect members of the public from litigation," said Lopez. "So they don't have to worry about injuring the person, if they're trying to do the right thing."
The American Heart Association offers resources and courses for hands-only CPR on their website.