If someone is on viagra (sildenafil) they cannot take nitroglycerin. so what would be given in an ambulance to a heart attack patient who regularly takes viagra (sildenafil)?

No easy answer: Based on BP and how frequent the patient is monitored and how active the chest pain. The key is drop in BP and that may cause more harm, Also viagra (sildenafil) has a short half-life, so if the patient took if many hours prior, and has a stable BP, NTG is an option, and then there is a hypertensive patient, NTG may be beneficial to get the BP down and decrease workload.