Tachycardia (fast heartbeat)

Sudden cardiac arrest (SCA)

  • 436,0001 lives are claimed by SCA in the United States every year. That’s equal to one life every 90 seconds1 or five football stadiums full of people.
  • Implantable cardioverter defibrillators (ICDs) are ~96% effective in treating dangerous ventricular arrhythmias.2–5


What is SCA?

SCA is an electrical problem with the heart that causes a dangerously fast heart rhythm (ventricular fibrillation). The rapid, irregular heart rhythm causes the heart to quiver rather than pump. When the heart stops pumping blood, oxygen cannot reach the body and brain. If not treated immediately, SCA is usually fatal.

Globally, cardiac arrest claims more lives than colorectal cancer, breast cancer, prostate cancer, influenza, pneumonia, auto accidents, HIV, firearms, and house fires combined.1

Differences between heart attack and SCA

SCA is not the same as a heart attack, although the two are often confused.

Think of your house: It needs plumbing and electricity to work as it should — and it has the potential for both plumbing and electrical problems. The same can happen with your heart. 

Illustration of home with numbers for blue electric line and pink water pipe plumbing below the house

1. SCA is an electrical issue.

SCA is a rhythm problem that prevents the heart from pumping blood to the brain and organs.

2. A heart attack is a plumbing issue.

A heart attack is typically caused by a blockage in a blood vessel to the heart muscle. This can permanently damage part of the heart and can lead to SCA.

What are symptoms of SCA?

  • Loss of consciousness
  • Dizziness
  • Fast heartbeat

What could put someone at risk of having SCA?

  • Previous heart attack or SCA
  • Family history of SCA or other heart disease
  • Heart failure
  • Low ejection fraction (this is explained below)
  • Rapid or abnormal heartbeats starting in the bottom chambers of the heart

Ejection fraction (EF) number

A number you should know.

EF is the percentage of blood that is pumped out of the heart with each heartbeat. Your doctor knows how well your heart is pumping based on your EF number. It is important for you and your doctor to check your EF regularly.

People with
a low EF are at
an increased
risk of SCA.6


Typical EF ranges7:


Heart’s pumping ability is NORMAL


Heart’s pumping ability is

40% or below

Heart’s pumping ability is

Treating SCA through defibrillation

Defibrillation involves delivering an electrical shock to your heart to restore a normal heartbeat. If not treated immediately, SCA can be fatal.
Automated external defibrillator (AED) inside a blue circle


An automated external defibrillator, or AED, is a portable device that measures the heart’s electrical activity. It is used by emergency response teams or the general public to shock the heart.

Evera™ implantable cardioverter defibrillator (ICD) with a lead encircled in blue


An ICD system has two parts: the defibrillator and the leads.

  • A defibrillator continuously monitors the heart and automatically corrects heart rhythms.
  • Leads are thin, soft, insulated wires about the size of a spaghetti noodle. They carry the electrical impulse from the ICD to your heart. They also send information about the heart’s natural activity back to the ICD.

Patient stories

Julie’s story

Julie suffered an SCA while celebrating her birthday and received an ICD. Watch the video to hear her story.

Steve’s story

Steve suffered an SCA while golfing with his daughter and received an ICD. Watch the video to hear his story.

Patient resources

pdf Discussion guide for patients: arrhythmias (.pdf)

Download this checklist to begin a conversation with your physician about your heart health.


pdf Are you at risk for SCA? (.pdf)

Download this brochure for more information on the symptoms and risks of SCA.


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Get Heart Device Answers.

Visit HeartDeviceAnswers.com, an interactive website full of questions and answers about living with a heart device.

Information on this site should not be used as a substitute for talking with your doctor. Always talk with your doctor about diagnosis and treatment information.



CPR Facts and Stats. American Heart Association. Available at: cpr.heart.org/en/resources/cpr-facts-and-stats. Accessed October 26, 2023.


Lambiase PD, Theuns DA, Murgatroyd P, et al. Subcutaneous implantable cardioverter-defibrillators: Long-term results of the EFFORTLESS study. Eur Heart J. 2022;43(21):2037–2050.


Larsen JM, Heath FP, Riahi S, et al. Single and dual coil shock efficacy and predictors of shock failure in patients with modern implantable cardioverter defibrillators-a single-center paired randomized study. J Interv Card Electrophysiol. 2019;54(1):65–72.


Knops RE, van der Stuijt W, Delnoy PPHM, et al. Efficacy and safety of appropriate shocks and antitachycardia pacing in transvenous and subcutaneous implantable defibrillators: Analysis of all appropriate therapy in the PRAETORIAN trial. Circulation. 2022;145(5):321–329.


Bänsch D, Bonnemeier H, Brandt J, et al. Shock efficacy of single and dual coil electrodes–new insights from the NORDIC ICD Trial. Europace. 2018;20(6):971–978.


Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/ HRS 2008 Guidelines for device-based therapy of cardiac rhythm abnormalities [corrections appear at J Am Coll Cardiol. April 21, 2009; 53(16):1473. J Am Coll Cardiol. January 6, 2009;53(1):147]. J Am Coll Cardiol. 2008;51(21):e1–62.