Cardiac arrest: adult not breathing

DRAFT: not yet checked against the sources. When in doubt, ask a doctor or rescuers.

First minutes

Check safety. Shake the shoulders, ask loudly: "Can you hear me?"
No answer: tilt the head back, lift the chin. Look at the chest for up to 10 seconds. Occasional gasps are not breathing.
Not breathing normally: send someone to call an ambulance and fetch a defibrillator (AED). Alone: speakerphone and start.
Hands stacked, centre of the chest, arms straight. Push 5-6 cm (2-2.4 in) deep, 100-120 per minute, let the chest rise fully.
If you can give breaths: 30 compressions, 2 breaths of 1 second. If not: compressions only, no pauses.
Defibrillator: switch it on and follow the voice. It is safe.
Do not stop until the person breathes, help arrives, or you are exhausted. Swap every 2 minutes.

× Stop to look for a pulse.
× Fear of hurting them: without help they die; broken ribs are no reason to stop.
× Hit the chest, give water to drink, pour water on them.
× Waste time on mouth-to-mouth if you hesitate: compressions matter most.

Tell the medics: when they collapsed, how long you pumped, whether an AED was used.

Source: ERC Guidelines 2021 Basic Life Support; check the numbers (5-6 cm, 100-120, 30:2). Children and infants: separate card (not written yet)