Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services if you or someone else has:
Fainted and is not recovering normally
Chest pain, severe shortness of breath, or sudden confusion
Collapse with no normal breathing
A very slow heartbeat with severe weakness, grey or blue skin, or difficulty staying awake
And for anyone, someone who:
has chest pain, tightness or pressure lasting more than a few minutes
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Seek prompt medical assessment if you have new fainting, repeated near-fainting, unexplained dizziness, or a slow pulse with weakness or breathlessness.
Do not drive yourself if you feel likely to faint.
And for anyone, someone who:
is getting rapidly more short of breath, or has gained several pounds in a few days with swelling
3
Does any of this apply?
Book an appointment
Arrange routine follow-up if previously mild symptoms become more frequent, your exercise tolerance falls, or a home monitor repeatedly reports an unusually slow rate.
If you have a pacemaker, contact your device clinic about redness, swelling, drainage, or increasing pain around the implant site, or if you receive a device alert.
The article also says
If someone is unresponsive and not breathing normally, begin cardiopulmonary resuscitation if you know how and use an automated external defibrillator if one is available.
Every sign above is quoted from the sofidex article on Heart block. If you are not sure, err upward — it is always reasonable to be checked.