In the final week of the regular season of National Football League play, millions of Americans have been relieved to learn that Buffalo Bills safety Damar Hamlin, 24, continues to be making progress as he recovers at the University of Cincinnati Medical Center.

Still in critical condition, he is said to be breathing on his own, with "excellent" neurological function, the Bills said in a statement released on Twitter on Saturday.

The star safety this past Monday night collapsed on the football field after what appeared to be a routine tackle during the first quarter of the game against the Cincinnati Bengals as millions watched in shock and dismay on national television.

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The medical staff on the field performed life-saving resuscitative measures, including cardiopulmonary resuscitation (CPR) with the use of an automated external defibrillator, or AED.

"Damar Hamlin suffered a cardiac arrest following a hit in our game versus the Bengals," the Buffalo Bills said in a statement this past Tuesday. 

"His heartbeat was restored on the field, and he was transferred to the UC [University of Cincinnati] Medical Center for further testing and treatment."

Encouraging news came overnight on Friday as his doctor said his breathing tube was removed and that he is neurologically intact. 

"Every second counts when sudden cardiac arrest occurs, and it’s critical to know what to do in an emergency," Dr. Nici Singletary, co-chair of the American Red Cross Scientific Advisory Council and professor in the department of emergency medicine at the University of Virginia, told Fox News Digital in an interview.

Here's a further dive into the medical issues surrounding what happened — and what to do in an emergency scenario.

"Cardiac arrest occurs when the heart stops beating or beats too ineffectively to circulate blood to the brain and other vital organs," Singletary added.

"It frequently happens suddenly and without any warning signs or symptoms." 

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A heart attack occurs, she said, when the cells in the part of the heart muscle are not receiving the oxygen and nutrients they need.

The cells become damaged and can die, which causes the heart to not pump normally — and in some situations, the heart can stop pumping completely. 

There are many medical and trauma emergencies that can cause cardiac arrest, including a heart attack.

If people out in public witness a cardiac arrest, Dr. Matthew Silvis, a sports medicine physician at Penn State Health in Pennsylvania, said it's key to remember two important points, 

"First, [there must be] quick recognition," he said. "If you don't consider cardiac arrest as a cause for collapse, you will miss an opportunity to intervene quickly."

He added, "We are trained in the medical profession when someone collapses to consider right away if there's a pulse or whether the person is breathing."

"Second, it is really important to prepare in advance for life-threatening emergencies," he said.

"Ideally you should have an emergency action plan in place and rehearsed," Silvis added.

Cardiac arrest is not the same as a heart attack, the Centers for Disease Control and Prevention (CDC) notes. 

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"A heart attack happens when blood flow to the heart is blocked. A person having a heart attack is still talking and breathing," the CDC says. "This person does not need CPR — but they do need to get to the hospital right away. Heart attack increases the risk for going into cardiac arrest."

CPR is a technique designed to resuscitate someone after the heart stops beating, according to the American Red Cross.

"If you see someone collapse and you don’t know CPR, call or have someone else call 911, start hands-only CPR and use an AED if one is available," Singletary told Fox News Digital. 

"Although a small percentage of people are up-to-date with CPR certification, most people (>50%) have had some training in their lifetime," Dr. Baljinder S. Sidhu of California told Fox News Digital. 

"In the event of witnessing a cardiac arrest, doing [hands-only] CPR can still double the chances of survival in most people," added Sidhu, a pulmonologist and sleep specialist and also the co-owner of Pacific Coast Critical Care Group in Southern California.

A bystander can do hands-only CPR without any training, he said.

"Most people who experience cardiac arrest at home, at work or in a public location die because they don't receive immediate CPR from someone on the scene," the American Heart Association noted on its YouTube channel. 

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"If you see a teen or adult suddenly collapse, call 911 and push hard and fast in the center of the chest to the beat of any tune that is 1000 beats per minute, such as the classic disco song ‘Stayin' Alive,’" the association added.

Another form of CPR involves not only hand compressions but also giving breath — but this form requires more practice and training. 

"The American Red Cross recommends lifesaving training for everyone," Singletary added.

"Training takes only a few hours and can give you the skills and confidence to act in an emergency and help save a life."

Here are steps to know.

Step 1: First, check the scene to make sure it’s safe.

Step 2: If the person is not responding, check for a pulse. See if the person is breathing by shouting, tapping, and shouting the person's name. 

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Step 3: If the person is unresponsive and not breathing or is only gasping, call or direct someone to call 911. Also, have another person get an AED, ideally. 

Step 4: Next, place the person on his or her back on a firm, flat surface, per the American Red Cross.

Step 5: Give 30 chest compressions by having two hands centered on the chest with shoulders directly over the hands while elbows are locked, per the American Red Cross website.

Try to compress at a depth of at least two inches at a rate of 100 to 120 compressions per minute, remembering to allow the chest to return to its normal position after each compression.

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Step 6: After 30 compressions, give two breaths.

"Open the airway to a past-neutral position using the head-tilt/chin-lift technique," per the American Red Cross website. The organization also recommends making sure each breath lasts approximately one second, causes the chest to rise with each breath and allows air to exit before starting the next breath.

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Step 7: Continue repeated sets of 30 chest compressions and two breaths until medical professionals arrive on the scene and can assume care, per the American Red Cross.

"CPR has changed over time," Silvis told Fox News Digital. "Chest compressions are really the focus now."

In the past, it was taught that for every two breaths a person should administer 15 compressions, Silvis added.

"Now, the ratio is taught as two breaths for every 30 compressions," he noted. "This increases the emphasis on chest compressions and takes it away from breathing."