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What is Ventricular Fibrillation?

What is Ventricular Fibrillation (VF)?

Ventricular fibrillation (VF) is a chaotic and disorganised heart rhythm originating in the ventricles (the lower heart chambers). Instead of contracting in a coordinated way, the ventricles quiver rapidly and ineffectively, so no blood is pumped to the brain or body. This results in sudden cardiac arrest. Without immediate treatment, VF is fatal within minutes

What’s happening inside the heart

  • Normal heartbeat: electrical signals spread smoothly, causing the heart to pump blood.
  • In VF: many abnormal impulses fire randomly, producing a very fast, irregular rhythm (>300/min).
  • On a monitor/ECG: VF looks like a wavy, irregular line with no recognisable QRS complexes.
  • It often starts as ventricular tachycardia (VT), and is a very rapid ventricular rhythm that often leads to inadequate perfusion and commonly degenerates into VF if untreated.

Signs and symptoms

Because circulation stops suddenly, a person in VF will:


  • Collapse without warning
  • No movement
  • Be unresponsive
  • Show no normal breathing (may have abnormal gasps initially)


This is a cardiac arrest situation.

Common causes and triggers

  • Heart attack (acute myocardial infarction) – the most common cause
  • Coronary artery disease or cardiomyopathy
  • Electrolyte imbalances (low potassium or magnesium)
  • Congenital or inherited electrical disorders (e.g. Long QT syndrome, Brugada syndrome)
  • Heart failure or structural heart disease
  • Toxins/medications (e.g. some antiarrhythmics, recreational drugs)
  • Severe hypoxia, trauma, electrical shock, drowning, commotio cordis