What are cardiac arrest, heart attack and heart failure?

Damar Hamlin continuing recovery in Buffalo Buffalo Bills safety Damar Hamelin has been transferred to a hospital in Buffalo to continue his recovery from a cardiac arrest.

Heart disease is a leading killer around the world and the top cause of death in the United States. It killed an estimated 17.9 million people in 2019, representing 32% of all deaths globally, according to the World Health Organization.

But not all heart disease is the same. It can affect the blood vessels to the heart or brain, heart muscles and valves, and other areas of the body. Cardiovascular diseases can require long-term treatment, or they can come on suddenly and seriously.

Buffalo Bills safety Damar Hamlin, 24, suffered a cardiac arrest and collapsed on the field during the first quarter of Monday night's game between the Bills and Cincinnati Bengals, his team said. It's not clear what caused his cardiac arrest.

WHAT IS CARDIAC ARREST?

Cardiac arrest results from electrical disturbances that cause the heart to suddenly stop beating properly.

In cardiac arrest, death can result quickly if steps aren't taken immediately. "Cardiac arrest may be reversed if CPR is performed and a defibrillator shocks the heart and restores a normal heart rhythm within a few minutes," according to the American Heart Association.

More than 350,000 cardiac arrests occur outside a hospital in the United States each year, the AHA said.

A sudden, unexpected loss of heart function also results in a sudden loss of breathing and consciousness.

Cardiac arrest is not the same as a heart attack, although almost any known heart condition, including heart attack, can cause cardiac arrest.

Another emergency that can lead to cardiac arrest, commotio cordis, is a disruption of heart rhythm after a blow to the area directly over the heart at a key time during a heartbeat cycle.

It's rare, but it mostly occurs in boys and young men during sports. The American Heart Association says it's the leading cause of deaths in youth baseball in the United States, typically two to three per year. Automated external defibrillators have helped increase the survival rate.

WHAT IS A HEART ATTACK?

Unlike cardiac arrest, a heart attack is a circulation problem. When circulation is blocked or cut off in some way and blood is no longer supplied to the heart muscle, this can damage that muscle -- it's commonly described as a heart attack; doctors may refer to it as "myocardial infarction."

Blockages causing heart attacks are mostly caused by a buildup of plaque in the arteries. Plaque forms when cholesterol combines with fat, calcium and other substances in the blood.

Combined, these elements harden into plaque, which can then rupture, causing a blood clot to form. Large clots can completely block the flow of blood through an artery.

"People who are at risk for heart attacks are people who have a family history of heart attack, having high cholesterol, high blood pressure, diabetes, lack of exercise, cigarette smoking -- the major risk factors we always discuss," Dr. Nieca Goldberg, medical director of Atria New York City and clinical associate professor of medicine at NYU Grossman School of Medicine, previously told CNN.

Another less frequent cause of a heart attack is a spasm caused by tobacco or possibly illicit drugs, such as cocaine, which disables the heart muscle, according to the American Heart Association. A tear in the artery, though rare, can also result in a heart attack.

Heart attacks can be fatal, but they do not automatically lead to death. Immediate emergency medical help can often prevent a serious outcome.

"If you think someone is having a heart attack, call 911. Don't wait," Goldberg said, explaining that the reason it's important to take an ambulance to the hospital instead of catching a ride with a family member or friend. An ambulance is equipped to offer treatment on the way to the hospital.

Common warning signs of a heart attack are discomfort or pain in the chest; discomfort in other areas of the upper body, including pain in in one or both arms, the back, neck, jaw or stomach; and shortness of breath. Other possible signs include cold sweat, nausea or light-headedness.

Overall, heart attacks are more common than cardiac arrest in the United States.

WHAT IS HEART FAILURE?

Heart failure is condition that occurs when the heart, essentially a pump, cannot effectively push blood out through the arteries and circulatory system to the body's other organs and tissues.

Congestive heart failure, a worsening of this general condition, means blood flow from the heart through the arteries has slowed while blood returning to the heart through the veins has begun to back up and combined they cause congestion -- a blood traffic jam -- in the body's tissues.

The result is edema, or swelling, usually in the legs and ankles, though edema can happen anywhere in the body. Heart failure also impairs the kidneys' ability to dispose of water and sodium, causing even more swelling. When pulmonary edema happens, fluid collects in the lungs and interferes with breathing.

Conditions that can lead to heart failure include high blood pressure, diabetes, obesity and coronary artery disease: when plaque builds up in the walls of arteries causing them to narrow and increasing the difficulty of pumping blood.

Heart failure is a medical condition that needs to be treated to prevent a life-threatening heart attack, but is not as immediately life threatening as heart attack or cardiac arrest.