"The biggest issue right now that he has circulation back is his brain," said Dr. Sean Swearingen, director of sports cardiology at Rush University Medical Center. "The brain within two to three minutes starts to develop permanent damage from not getting oxygen."
Damar Hamlin's uncle says he was resuscitated twice after collapse
The scene that played out of the field brought Elston Harris right back to the morning of June 23, 2016, when he went into cardiac arrest on the basketball court during a pickup game.
"A few exchanges of conversation and playing basketball and I fell back and hit the floor," he recalled.
READ MORE: Doctor discusses injury to Buffalo Bills' Damar Hamlin
An off-duty Chicago police officer who was playing with Harris immediately performed CPR for 10 minutes. The procedure revived him, and he was rushed to Advocate Trinity Hospital.
His cardiologist, Dr. Marlon Everett, said both Harris and Hamlin likely would have died without CPR, which is only administered when the heart is no longer beating.
How important is CPR and AED training?
"In the real world, usually there are not medical professionals, I think it's important for most laymen to learn CPR at least the basics," Everett said.
Everett and Harris teamed up to start a program called Athletes for CPR, which trained students and adults.
"We were all through the public school system, the park districts and churches," Harris said.
"It doesn't take long to learn and it can save the life of so many," said Everett.
To perform CPR, you should interlock one hand on top of the other. Compressions should be two and a half inches deep into the chest; you don't want to bend your arms but rather put the weight of your whole body to compress the heart.
Compressions should be done at a steady rate of 100-120 compressions per minute.
The Athletes for CPR program through Advocate Trinity Hospital was temporarily put on hold during the pandemic, but will resume in the spring.