SYRACUSE, N.Y. (WSYR-TV) — Damar Hamlin’s teammates knelt around the Bills’ safety after he went into cardiac arrest following a hit in last night’s game against the Bengals.

Dr. Dana Aiello, a cardiologist and assistant professor of medicine at Upstate University Hospital, explains what happens during cardiac arrest.

Cardiac arrest is where the heart is not pumping effectively to perfuse or to send blood to the organs, more specifically the brain.

Dr. Aiello explained.

How can a hit lead to cardiac arrest?

“It’s generally safe from a cardiac perspective, because the heart is contained in the chest wall and surrounded by protective mechanisms,” said Dr. Aiello.

He said there’s been a lot of speculation that the 24-year-old could have commotio cordis, which is rare, but happens.

When there’s trauma to the chest wall and to the heart at an exact time in the electrical cycle of the heart, that causes the heart to beat. That’s a very minute amount of time about 20 to 40 milliseconds.

said Dr. Aiello.

It’s unclear what led to Hamlin’s cardiac arrest.

The Bills tweeting, “…His heartbeat was restored on the field and he was transferred to the UC Medical Center for further testing and treatment.”

Dr. Aiello said early and good quality CPR is crucial and something we all should learn.

“It has saved countless lives, being able to recognize when somebody’s not breathing, when someone does not have a pulse, to start CPR and activate that emergency response as quickly as possible.”

Dr. Dana Aiello, Upstate University Hospital Cardiologist & Assistant Professor of Medicine

If you would like to be trained in CPR, you can find a course near you through the American Heart Association or the Red Cross.

The American Heart Association demonstrates Hands-Only CPR here.