PORTLAND, Ore. (KOIN) — Dr. Charles Henrickson was watching the Monday Night Football game between the Buffalo Bills and Cincinnati Bengals when Bills safety Damar Hamlin collapsed and went into cardiac arrest.

Henrickson, a cardiologist/heart rhythm specialist at OHSU, saw the emergency medical teams administer CPR to the 24-year-old to get oxygen to the brain and lungs when your heart stops.

“The easy way to remember that is your ABCs — your airway, your breathing and your circulation, which is your pulse. You check those 3 things and if there’s no breathing, then you start CPR,” Henrikson said.

Cardiac arrest is not the same as a heart attack. Sudden cardiac arrest is tied to the heart’s electrical impulses getting interrupted as it beats. A heart attack is a circulation problem, when blood flow to the heart is blocked.

More than 365,000 people a year in the US have sudden cardiac arrest.

Hamlin was involved in a seemingly routine tackle. He stood up after the tackle, then immediately collapsed motionless on the field.

Commotio Cordis, a blow to the chest causes the heartbeat to quiver and go into sudden cardiac arrest when the hit occurs directly over the heart at the wrong time during the heart’s rhythm cycle.

It’s quite rare. Athletes are often hit by a ball or an opponent in the chest.

There is also the possibility of an underlying heart condition that was previously detected.

American Heart Association – How to do CPR

At this time, Hamlin remains in critical condition in the ICU. What kept Hamlin alive, doctors said, was the quick CPR and the use of an AED to shock the heart back into a normal rhythm.

The takeaway: Learn CPR and don’t be afraid to step up if someone might need it.