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When someone has a cardiac arrest, their heart stops beating. This means blood doesn't get pumped around their body and oxygen doesn't reach their brain and other organs. If a person's heart stops beating for more than a few minutes, they are unlikely to recover.

To understand what happens during a cardiac arrest, it helps to know a little bit about the heart. To read more, see How your heart works.

Before a person has a cardiac arrest, their heart beats abnormally. Two things can happen.¹

• Their heart beats fast (150 to 200 beats a minute) and the beats start in the lower chambers (ventricles) of the heart, instead of the upper chambers. Doctors call this pulseless ventricular tachycardia.
• Their heart beats very fast (more than 300 beats a minute) and very irregularly. The beats start in the ventricles, instead of the upper chambers. Doctors call this ventricular fibrillation.

If a person's heart beats like this, blood isn't pumped to their lungs, the rest of their body, and back to their heart. If no blood is coming back into the heart, it stops beating. This is a cardiac arrest.

You are more likely to have a cardiac arrest if:¹

• You have heart disease
• You've had a heart attack
• You have heart failure
• You're middle aged or older
• You're a man.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.