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Heart attack or cardiac arrest: what to do now

Heart attack signs and cardiac arrest signs, what the sources say to do, and what CPR and an AED are. It does not replace emergency care.

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Signs of a heart attack

  • Chest discomfort, often in the center or on the left side of the chest, is among the most common signs.1
  • Chest discomfort can feel like pressure, squeezing, fullness or pain, or it can feel like heartburn or indigestion.1
  • Chest discomfort usually lasts longer than a few minutes, and it may go away and come back.1
  • Shortness of breath is also one of the most common signs, and sometimes it is the only symptom.1
  • Shortness of breath can come before or during chest discomfort, and it can happen at rest or with a little physical activity.1
  • Pain or discomfort in the upper body is another of the most common signs, felt in one or both arms, the back, the shoulders, the neck, the jaw or the upper stomach.1
  • Other signs include nausea, vomiting, dizziness, lightheadedness, a racing or pounding heart and a cold sweat.1
  • Women’s symptoms sometimes differ from men’s, and women are more likely to feel tired for no reason.1
  • Symptoms range from mild to severe, and they can differ from one person to the next.1

“If you are having symptoms of a heart attack, you should call 911, even if you are not sure it is a heart attack.”2

“it's important to know the symptoms of a heart attack and call 911 if you or someone else is having them.”2

U.S. National Library of Medicine (MedlinePlus), Heart Attack (MedlinePlus health topic)

In an emergency, call your local emergency number.

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Signs of sudden cardiac arrest (SCA)

  • Loss of consciousness, or fainting, is usually the first sign of cardiac arrest.3
  • Some people feel dizzy or light-headed, or notice a racing heartbeat, shortly before they faint.3
  • In the hour before cardiac arrest, some people have chest pain, shortness of breath, nausea or vomiting.3

“Call 9-1-1 right away if someone has signs or symptoms of SCA.”4

“The sooner you call for help, the sooner lifesaving treatment can begin.”4

U.S. National Library of Medicine (MedlinePlus), Sudden Cardiac Arrest (MedlinePlus health topic)

In an emergency, call your local emergency number.

More about signs, from NHLBI

  • NHLBI says heart attack symptoms can build slowly, can be mild or sudden, and can start and stop over a span of several hours.5
  • NHLBI says symptoms differ from person to person and between men and women, and may differ in a second heart attack.5
  • NHLBI says a heart attack can cause no symptoms, or only mild ones, which it names a silent heart attack.6
  • NHLBI links shortness of breath at rest or with light activity more closely to older adults, and unusual tiredness that can last for days more closely to women.7
  • NHLBI lists a sudden collapse with loss of consciousness as a sign of cardiac arrest.8
  • NHLBI also lists not breathing, ineffective breathing, and gasping for air.8
  • NHLBI adds no response to shouting or shaking, and no pulse, to its list.8
  • NHLBI says that most people with a cardiac arrest are not treated in time to survive.9

How a heart attack and cardiac arrest differ

  • In a heart attack, blood flow to the heart suddenly becomes blocked.2
  • If a heart attack is not treated quickly, heart muscle starts to die.2
  • Quick treatment may prevent or limit damage to the heart muscle.2
  • During a heart attack, the heart usually does not suddenly stop beating.2
  • MedlinePlus says that in a sudden cardiac arrest "the heart stops beating and the person passes out".2
  • MedlinePlus uses the short form SCA for sudden cardiac arrest.10
  • When the heart stops, vital organs, including the brain, no longer get blood.10
  • Without treatment, cardiac arrest usually causes death within minutes.10
  • MedlinePlus also says cardiac arrest happens without warning and needs emergency treatment.11
  • A heart attack can trigger a sudden cardiac arrest, and MedlinePlus describes both as medical emergencies.2

What CPR is

  • CPR stands for cardiopulmonary resuscitation.10
  • CPR helps blood keep moving to the brain and other organs until the heart’s rhythm is restored.4
  • MedlinePlus says "CPR should be started right away and continued until a defibrillator is ready to use."4
  • MedlinePlus says that a person who has not been trained in CPR "can still help by giving hands-only CPR".12
  • MedlinePlus says hands-only CPR is done by "pushing hard and fast on the center of the chest".12

What an AED is

  • AED stands for automated external defibrillator.12
  • A defibrillator gives the heart an electric shock.4
  • The shock can bring back a normal rhythm in a heart that has stopped beating.4
  • According to MedlinePlus, the shock needs to come within minutes of the cardiac arrest to work well.4
  • MedlinePlus says many public places, such as schools, businesses and airports, have AEDs.12
  • MedlinePlus says people without training can use an AED, and that it gives step-by-step voice instructions.12
  • An AED gives a shock if it detects a dangerous irregular heartbeat, which prevents a shock to someone who may have only fainted.12
  • MedlinePlus says most police officers, emergency medical technicians and other first responders are "trained and equipped to use a defibrillator".4
  • NHLBI says using an AED is not difficult, and that training helps a great deal.13
  • NHLBI also says AED training often comes with CPR training, and that classes are offered by many major health groups.13
  • MedlinePlus says people at risk of cardiac arrest "may want to consider having an AED at home".12
  • NHLBI says providers sometimes advise an AED at home when a person’s risk of cardiac arrest is high.14

One cardiac arrest risk that MedlinePlus names

  • Most people with cardiac arrest have coronary artery disease, which usually causes no symptoms.15

Topics from the NHLBI cardiac arrest page

  • The signs of cardiac arrest.13
  • Where AEDs are kept in offices, schools and other public places.13
  • How to use an AED, including classes from major health organizations.13

Questions to ask

  1. Can a heart attack happen with no symptoms, or only very mild ones?
  2. Which heart attack symptoms are more common in women, and which in older adults?
  3. Does my heart health put me at a higher risk of cardiac arrest?
  4. Would an AED at home make sense for someone with my heart condition?
  5. Where can I learn CPR and how to use an AED?

Sources

  1. Heart Attack (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, heart attack symptoms. Retrieved .
  2. Heart Attack (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, what is a heart attack. Retrieved .
  3. Sudden Cardiac Arrest (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, what are the symptoms of sudden cardiac arrest (SCA). Retrieved .
  4. Sudden Cardiac Arrest (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, what are the treatments for sudden cardiac arrest (SCA). Retrieved .
  5. Heart Attack: Symptoms (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, introduction. Retrieved .
  6. Heart Attack: Symptoms (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, silent heart attacks. Retrieved .
  7. Heart Attack: Symptoms (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, symptom list. Retrieved .
  8. Cardiac Arrest: What Is Cardiac Arrest? (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, signs of cardiac arrest. Retrieved .
  9. Cardiac Arrest: What Is Cardiac Arrest? (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, what is cardiac arrest. Retrieved .
  10. Sudden Cardiac Arrest (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, what is sudden cardiac arrest (SCA). Retrieved .
  11. Sudden Cardiac Arrest (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, how is sudden cardiac arrest (SCA) diagnosed. Retrieved .
  12. Sudden Cardiac Arrest (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, what should I do if I think that someone has had an SCA. Retrieved .
  13. Cardiac Arrest: What Is Cardiac Arrest? (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, AED section. Retrieved .
  14. Defibrillators: What Are Defibrillators? (NHLBI) Webpage, National Heart, Lung, and Blood Institute (NIH), Page body, types of defibrillators. Retrieved .
  15. Sudden Cardiac Arrest (MedlinePlus health topic) Webpage, U.S. National Library of Medicine (MedlinePlus), Summary, who is at risk for sudden cardiac arrest (SCA). Retrieved .

About this guide

Written for
Adults, and the people with them
What it covers
Written from two MedlinePlus health topic pages and three NHLBI pages that are restated in the atlas’s own words. The sources are US government pages, and their emergency wording is US wording.
Pages it explains
Sources checked
2026-10-15
Next check due
2027-04-15
Reading level
Estimated grade 7.0 (target 7)

Every sentence cites a source. Words in quotation marks are the source's own; the rest is the atlas's summary.

https://cardio.openmedicalatlas.org/guides/heart-attack-or-cardiac-arrest-what-to-do-now/ · Release 73130c34862e2d06, built 2026-10-15