What does asystole mean?
Asystole is a noun referring to the total absence of electrical activity in the heart, which causes the heart muscle to stop contracting altogether. In practical terms, it represents a state of cardiac standstill — the heart produces no pumping action and an electrocardiogram shows a flat line rather than any recognisable rhythm. The word belongs almost entirely to medical language, appearing most often in cardiology, anaesthesia, and emergency medicine, where clinicians classify it as one of the non-shockable rhythms during cardiac arrest. This point carries real significance: because there is no disorganised electrical activity to correct, defibrillation cannot treat asystole, and management instead relies on chest compressions, adrenaline, and identifying underlying causes such as hypoxia or blood loss. For general readers, asystole is worth knowing both as precise vocabulary — distinct from cardiac arrest more broadly — and because it names the clinical reality behind the familiar dramatic image of the flatlining monitor.
nounThe absence of electrical activity in the heart, resulting in the heart's failure to contract; in clinical terms, a state of cardiac standstill.
- Complete cessation of the heartbeat due to absence of electrical activity in the heart.
"The monitor showed flatline asystole, and the resuscitation team began compressions immediately."
"The electrocardiogram confirmed asystole, with no discernible rhythm on the tracing."
"Despite prolonged efforts, the patient's asystole could not be reversed."
Rarely used; the term typically denotes a clinical state rather than a countable event, so singular usage predominates even when discussing multiple episodes.
"The patient experienced recurrent asystoles during monitoring."
On a hospital monitor, asystole is that dreaded flatline — but shockingly (literally), defibrillators can't fix it: electricity won't restart a heart that has none.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of asystole
Asystole derives from Greek roots: the prefix a- meaning 'without', combined with systole, from Greek systolē, meaning 'contraction'. It entered medical Latin before passing into English medical usage, becoming established in clinical literature by the 19th century as physicians sought precise terminology for cardiac failure. It shares its root with systole itself and its antonymic counterpart diastole, both foundational terms in describing the cardiac cycle.
Related word forms
How asystole is actually used
Strictly a medical term used in clinical, emergency-medicine, and cardiology contexts rather than everyday speech. In lay usage it is often loosely equated with 'flatline' or 'cardiac arrest', though clinicians reserve it for one specific arrestable rhythm. Plural is rare because the condition is treated as a state.
Easily confused with asystole
Asystole is one specific cause of cardiac arrest — the complete absence of heart electrical activity — whereas cardiac arrest is the broader term for any sudden cessation of effective heart function, including arrhythmias like ventricular fibrillation.