Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for new, severe, or unexplained chest pain, especially if it feels like pressure, squeezing, or heaviness.
This is particularly important if the discomfort spreads to your arm, jaw, back, or shoulder, or occurs with breathlessness, sweating, faintness, weakness, or nausea.
Emergency assessment is also appropriate if you vomit blood, vomit material resembling coffee grounds, or pass black, tar-like stool.
These can be signs of bleeding in the digestive tract.
And for anyone, someone who:
Do not wait to see whether an antacid helps.
Seek same-day medical advice if swallowing becomes difficult or painful, food feels stuck, or you are vomiting repeatedly.
Prompt assessment is also important if you cannot keep fluids down.
And for anyone, someone who:
Book a routine appointment if heartburn keeps returning, affects sleep or daily activities, or continues despite appropriate non-prescription treatment.
You should also arrange an appointment if you have unexplained weight loss, ongoing nausea, a persistent cough or hoarse voice, or regularly need medicine to control symptoms.
Every sign above is quoted from the sofidex article on Heartburn. If you are not sure, err upward — it is always reasonable to be checked.