What should i do if i start to feel chest pains while on a plane. is there any preventative steps i should take before international flight?

Tell flight steward: If you develop concerning chest symptom, tell a flight attendant immediately. They should have some basic medical training and per report, they have some medical equipment. Make sure you have your medications with you especially if you have nitroglycerin. Before a long flight, ensure well hydrated, move your legs when possible (avoid blood clots), and ask your doc if Aspirin is good for you.