Final answer:
Patients are often instructed by physicians to take up to three doses of nitroglycerin for angina before calling for emergency services if symptoms do not improve.
Step-by-step explanation:
Most patients are instructed by their physician to take up to three doses of nitroglycerin before calling Emergency Medical Services (EMS). Nitroglycerin is typically used to treat episodes of angina (chest pain) and is often recommended for patients with known heart conditions. The standard protocol generally advises taking one dose every five minutes. If the symptoms do not improve after three doses taken five minutes apart, it is important to call EMS immediately as it may indicate a heart attack or other serious condition.