Each year, more than 356,000 people suffer a sudden cardiac arrest. Roughly 90 percent of these people do not survive. Many of those who suffer a cardiac arrest have what is called asystole. 

Having a better understanding of cardiac asystole can save lives and help you better grasp how the heart functions.

What Is Cardiac Asystole or Flatline? 

Put simply, cardiac asystole means the heart is not beating. On a heart monitor, the heartbeat would appear like a flat line. This is where the term “flatline” comes from. That line indicates that there is no electrical activity in the heart. 

Electrical activity triggers the heart muscle to contract. Those contractions push blood out to the rest of the body. If it is oxygenated, the blood goes from the left side of the heart to the body. If it is unoxygenated, it goes from the right side of the heart to the lungs. When someone is in cardiac asystole, there is no electrical activity. Therefore, no muscle contraction and no blood flow from the heart. The word ‘asystole’ appropriately comes from the Latin word meaning “lack of contraction”. 

Can You Survive Cardiac Asystole? 

People do survive cardiac systole, but it is rarer than what you see with other forms of cardiac arrest. Currently, about two percent of people survive cardiac asystole. Chances of survival depend greatly on what caused the problem with the heart. 

Asystole is considered a “non-shockable rhythm”. This means that using an AED (automated external defibrillator) to jump-start the heart will not work. CPR and medicines, like epinephrine, are used to help the person survive the asystole. 

Warning Signs and Symptoms

The signs of cardiac asystole are sudden collapse with loss of consciousness, loss of movement, and no pulse. Asystole may occur more suddenly compared to other types of cardiac arrest. It is important to recognize the signs of asystole. The sooner medical personnel are called, the sooner they can make efforts to revive the patient.

The general signs of a cardiac arrest include:

  • Lightheadedness
  • Vision changes (such as blurry vision)
  • Heart palpitations or fluttering
  • General weakness
  • Chest pain or tightness
  • Shortness of breath
  • Sweating
  • Nausea

For some, sudden cardiac arrest occurs with no warning. Whenever there is chest pain, it is better to get help immediately and rule out a heart problem. 

Causes and Risk Factors

Asystole occurs when there is an interruption or pause in the electrical activity to the heart. Many things can cause this, such as:

  • Weak or damaged heart muscle
  • Heart attack
  • Genetic conditions (such as long QT syndrome)
  • Medications
  • Poisons
  • Electrolyte imbalance
  • Sepsis (a severe and systemic infection)
  • Drug use
  • Inflammatory diseases such as sarcoidosis
  • Low blood flow or oxygen
  • Hypothermia


A cardiac monitor confirms the diagnosis of cardiac asystole. As mentioned earlier, asystole is a lack of electrical activity in the heart so the monitor will show a flat line without measurable heart beats. The person will not have a pulse, however patients with other types of cardiac arrest also do not have a pulse. 


The treatment for cardiac asystole is to correct the underlying problem causing it. As in other cardiac arrests, treatment for asystole includes CPR and medications. CPR attempts to simulate a heart beat and pump blood to the body while medical personnel work to identify and fix the problem causing the cardiac arrest. 

The medications used are typically called vasopressors or “pressors”. An example is epinephrine, or adrenaline. Epinephrine increases blood flow to the heart and the brain. Neither CPR nor vasopressors cure asystole by themselves. 

Asystole and Sudden Cardiac Arrest

Asystole is one type of cardiac arrest. In this type, the heart's electrical does not produce heart beats to pump blood to the body. The absence of a heartbeat cannot be treated with an AED by shocking the patient. Instead, CPR and medicines are administered while the cause of the asystole is determined and treated. 

The more you know about sudden cardiac arrest, the better the chance of getting help while there is still a shockable rhythm and before asystole occurs. Learn more about Sudden Cardiac Arrest.