Female paramedic taking a man's vitals

How to Treat Cardiac Arrest

Learn How EMTs & Paramedics Identify, Treat, and Care for Patients with Cardiac Arrest

Female paramedic taking a man's vitals

Cardiac arrest is one of the top 15 most common emergencies that EMS professionals respond to, accounting for about 2% of all EMS calls.

(Click here for our list of the most common EMS Emergencies for EMTs and Paramedics).

Cardiac arrest is the abrupt loss of heart function, breathing, and consciousness. The condition typically results from a problem with the heart’s electrical system, which disrupts the heart’s pumping action and stops blood flow to the body.

If not treated immediately, cardiac arrest can result in death. Survival is possible with immediate, appropriate medical care. Cardiopulmonary resuscitation (CPR), using a defibrillator — or even just giving compressions to the chest — can improve the chances of survival until emergency workers arrive.

In the United States, about 535,000 cases of cardiac arrest occur a year. About 61% of cardiac arrests occur outside of a hospital setting, while 39% occur within a hospital. Cardiac arrest becomes more common with age, and it affects males more often than females. The percentage of people who survive out of hospital cardiac arrest with treatment by emergency medical services is only about 8%.

Cardiac Arrest Definition

What is Cardiac Arrest?

Cardiac arrest is a sudden loss of blood flow resulting from the heart’s failure to pump effectively. Signs of cardiac arrest occurring include loss of consciousness and abnormal or absent breathing. Some individuals may experience chest pain, shortness of breath, or nausea before cardiac arrest. If not treated within minutes, it typically leads to death.

Signs and Symptoms Cardiac Arrest

About 50 percent of cardiac arrests are not preceded by any warning symptoms. Those who experience symptoms will be non-specific, such as new or worsening chest pain, fatigue, blackouts, dizziness, shortness of breath, weakness, and vomiting.

When cardiac arrest occurs, the most obvious sign of its occurrence will be the lack of a palpable pulse in the victim. Also, as a result of losing blood to the brain, the victim will rapidly lose consciousness and stop breathing.

The main symptom for diagnosing a cardiac arrest—as opposed to respiratory arrest, which shares many of the same symptoms—is lack of circulation.

Prompt intervention can often reverse a cardiac arrest, but death is all but certain without prompt treatment. In certain cases, cardiac arrest is an anticipated outcome of a serious illness where death is expected.

Signs and Symptoms of Cardiac Arrest Include:

  • Sudden collapse
  • No pulse
  • No breathing
  • Loss of consciousness

Signs and Symptoms Occurring Before Cardiac Arrest Include:

  • Chest discomfort
  • Shortness of breath
  • Weakness
  • Fast-beating, fluttering or pounding heart (palpitations)

Note: Cardiac arrest is not preceded by any warning symptoms in approximately 50 percent of people.

Causes of Cardiac Arrest

Cardiac arrest can be caused by almost any known heart condition. Most cardiac arrests occur when a diseased heart’s electrical system malfunctions. This malfunction causes an abnormal heart rhythm such as ventricular tachycardia (fast heartbeat), bradycardia (extremely slow heartbeat), or ventricular fibrillation (erratic heartbeat; quivering or fluttering). All of these irregular heartbeats are life-threatening.

The most common cause of cardiac arrest is coronary artery disease.

Less common causes of cardiac arrest include:

  • Major blood loss
  • Lack of oxygen
  • Very low potassium
  • Heart failure
  • Intense physical exercise
  • A number of inherited disorders, including long QT syndrome.

The initial heart rhythm is often ventricular fibrillation—which is an abnormal heart rhythm where the heart quivers instead of pumping blood normally. The diagnosis is confirmed by finding no pulse. While a cardiac arrest may be caused by heart attack or heart failure, the two conditions are not the same.

African-American paramedic standing by an ambulance

Other causes of cardiac arrest include:

  • Scarring of the heart tissue: A heart that has been scarred or enlarged from any cause, including a heart attack, is prone to develop life-threatening ventricular arrhythmias. The first six months after a heart attack is a high-risk period for sudden cardiac arrest in patients with atherosclerotic heart disease.
  • Thickened heart muscle (cardiomyopathy): Cardiomyopathy causes the heart muscle to become enlarged, thick, or rigid. This damage can be the result of high blood pressure, heart valve disease, or other causes.
  • Heart medications: Some heart medications can set the stage for arrhythmias that cause sudden cardiac arrest. Some drugs that treat arrhythmias can produce ventricular arrhythmias even at normal doses. Significant changes in blood levels of potassium and magnesium (from using diuretics, for example) can also cause life-threatening arrhythmias and cardiac arrest.
  • Electrical abnormalities: Electrical abnormalities, including Wolff-Parkinson-White syndrome and Long QT syndrome, can cause sudden cardiac arrest in children and young people.
  • Blood vessel abnormalities: Though rare, abnormal blood vessel conditions can occur in the coronary arteries and aorta. Adrenaline released during intense physical activity can trigger sudden cardiac arrest when these abnormalities are present.
  • Recreational drug use: With recreational drug use, cardiac arrest can occur in otherwise healthy people.

Mnemonic for reversible causes

“Hs and Ts” is the name for a mnemonic used to aid in remembering the possible treatable or reversible causes of cardiac arrest.


  • Hypovolemia — A lack of blood volume
  • Hypoxia — A lack of oxygen
  • Hydrogen ions (acidosis) —An abnormal pH in the body
  • Hyperkalemia or Hypokalemia — Both increased or decreased potassium can be life-threatening
  • Hypothermia — a low core body temperature
  • Hypoglycemia or Hyperglycemia — Low or high blood glucose


  • Tablets or Toxins — Such as drug overdose
  • Cardiac Tamponade — Fluid building up around the heart
  • Tension pneumothorax — A collapsed lung
  • Thrombosis (Myocardial infarction) — Heart attack
  • Thromboembolism (Pulmonary embolism) — A blood clot in the lung
  • Traumatic cardiac arrest

What’s The Difference Between a Cardiac Arrest and a Heart Attack?

No. Heart attack is not another term for cardiac arrest. Although a heart attack may cause cardiac arrest, the two conditions are actually different.

A heart attack is caused by a blockage that stops blood flow to the heart, and it is a problem with the victim’s circulation. In a heart attack, heart muscle dies due to the loss of blood supply. A heart attack is a serious, sometimes fatal condition.

Cardiac arrest, on the other hand, is caused when the heart’s electrical system malfunctions, causing the heart to stop beating properly. The heart’s pumping action is stopped or “arrested.”

When to Call 911 for Cardiac Arrest

These are the warning signs of cardiac arrest:

  • Sudden loss of responsiveness. The person does not respond to your voice or touch. Even if you tap them on the shoulders or ask loudly if they’re okay. The person does not move, speak, blink, or otherwise react.
  • No normal breathing. The victim isn’t breathing normally or is only gasping for air. Even after you tilt the head up and check for at least 5 seconds, breathing is not normal.

Close up of an EMT patch

Call 911 if you or someone you are with experiences any of these signs and symptoms:

  • Chest pain or discomfort
  • Heart palpitations
  • Rapid or irregular heartbeats
  • Unexplained wheezing
  • Shortness of breath
  • Fainting or near fainting
  • Lightheadedness or dizziness

How to Treat Cardiac Arrest

  • Call 911 immediately. If you suspect someone is experiencing cardiac arrest, call 911 immediately—before you begin CPR. If someone else can call 911 immediately, then begin CPR.
  • Perform CPR. Quickly check the person’s breathing. If the person isn’t breathing normally, begin CPR. Push hard and fast on the person’s chest—at the rate of 100 to 120 compressions a minute. If you’ve been trained in CPR, check the person’s airway and deliver rescue breaths after every 30 compressions.
    • If you haven’t been trained, just continue chest compressions. Allow the chest to rise completely between compressions. Keep doing this until a portable defibrillator is available or emergency workers arrive.
  • Use a portable defibrillator if one is available. It will give you step-by-step voice instructions. Continue chest compressions while the defibrillator is charging. When charged, the defibrillator will check the person’s heart rhythm and recommend a shock if needed. Deliver one shock if advised by the device and then immediately resume CPR, starting with chest compressions, or give chest compressions only, for about two minutes.
    • Using the defibrillator, check the person’s heart rhythm. If necessary, the defibrillator will give another shock. Repeat this cycle until the person recovers consciousness, or emergency workers take over.

How to Prevent Cardiac Arrest

Prevention strategies for cardiac arrest include not smoking, physical activity, and maintaining a healthy weight. Among those who survive cardiac arrest, targeted temperature management may improve outcomes. An implantable cardiac defibrillator may be placed to reduce the chance of death from recurrence.

How Do EMTs & Paramedics Treat Cardiac Arrest?

In the event of a cardiac arrest emergency, an EMT or paramedic will likely be the first healthcare provider to assess and treat your condition. EMTs have a clear set of protocols and procedures for most of the 911 emergencies they encounter, including cardiac arrest. For any suspected cardiac arrest, the first step is a rapid and systematic assessment of the patient. For this assessment, most EMS providers will use the ABCDE approach.

ABCDE stands for Airway, Breathing, Circulation, Disability, and Exposure. The ABCDE approach is applicable in all clinical emergencies for immediate assessment and treatment. It can be used in the street with or without any equipment. It can also be used in a more advanced form where emergency medical services are available, including emergency rooms, hospitals, or intensive care units.

Treatment Guidelines & Resources for Medical First Responders

The National Model EMS Clinical Guidelines by the National Association of State EMT Officials (NASEMSO) provides treatment guidelines for cardiac arrest on page 109. These guidelines are maintained by NASEMSO to facilitate the creation of state and local EMS system clinical guidelines, protocols, and operating procedures. These guidelines are either evidence-based or consensus-based and have been formatted for use by EMS professionals.

The guidelines include the following patient assessment:

  1. The patient in cardiac arrest requires a prompt balance of treatment and assessment
  2. In cases of cardiac arrest, assessments should be focused and limited to obtaining enough information to reveal the patient is pulseless
  3. Once pulselessness is discovered, treatment should be initiated immediately, and any further history must be obtained by bystanders while treatment is ongoing

Male paramedic assisting a patient

EMS Protocol for Cardiac Arrest Emergencies

Protocols for prehospital treatment of cardiac arrest vary by EMS provider and can also depend on the patient’s symptoms or medical history. Below is a sample protocol for prehospital treatment of cardiac arrest for patients with a suspected COVID-19 infection.

  • For patients WITHOUT suspicion of COVID-19 infection, for example, a sudden collapse in someone who is otherwise well, follow usual Statewide Cardiac Arrest Protocols.
  • For patients with known recent history of respiratory illness and fever or possible COVID-19 infection, treat according to Statewide Cardiac Arrest Protocols, AND:
    • If available, place a clear drape (medical drape, shower curtain, or drop cloth) over the patient’s face and head to reduce exposure to aerosolized secretions.
      • BVM ventilation and advanced airway placement can occur under the drape.
      • CAUTION – FIRE RISK: Most of these patients should not have a shockable rhythm, but if using a drape, ensure that it does not accumulate oxygen and that defibrillation pads are not under the drape during defibrillation.
      • After call, dispose of drape as if contaminated.
    • Attach a viral HEPA filter between the bag-valve and any ventilatory device (BVM mask or advanced airway). There is controversy about the risk of aerosol when comparing placing an endotracheal tube versus ventilating through an alternative airway. Placing an alternative airway under a clear drape may have the least risk of aerosol. EMS agency medical directors should define the expectation for advanced airway management in these patients.
    • When CPR is being performed, only necessary personnel should be next to the patient. Personnel should distance themselves when not performing interventions.
    • If no ROSC within 10 minutes of resuscitation, contact medical command for possible termination of resuscitation orders.
    • Patients in continuous cardiac arrest WILL NOT BE TRANSPORTED, regardless of mechanical CPR device. Resuscitation will either be terminated on scene, or ROSC sustained (continued palpable pulse and systolic BP≥60 mmHg for >10 minutes) BEFORE moving the patient to the patient compartment of an ambulance.
  • For witnessed arrests inside the patient care compartment:
    • Pull vehicle to a safe space to park and perform resuscitation in full PPE, with door OPEN.
    • If close to the receiving facility, medical command may order continued transport to the hospital, as long as all personnel in the patient compartment have sufficient full PPE (including N95 mask or equivalent) in place.
    • Field termination in the back of the ambulance by medical command order is valid and should be considered if no ROSC after CPR for >10 minutes with non-shockable rhythm in a patient with suspected COVID-19 infection. If this occurs, as with other field termination, contact the county coroner/medical examiner before moving for direction on destination.

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