While awaiting dental treatment, a patient experiences sudden chest pain lasting about 3 minutes. This is most likely to be:

The situation described—sudden chest pain lasting approximately 3 minutes—aligns closely with angina pectoris, which is characterized by transient chest pain caused by reduced blood flow to the heart muscle. Angina typically occurs during physical exertion or emotional stress and can subsist after rest or medication such as nitroglycerin.

The transient nature of the pain, lasting only a few minutes, suggests it is not a myocardial infarction or heart attack, which usually presents with more prolonged pain and may involve other symptoms such as nausea, sweating, or an overwhelming sense of impending doom. Additionally, allergies would not generally cause chest pain in the context described. Thus, in understanding the nature and duration of the symptoms, angina is the most fitting diagnosis in this scenario.