If i was born with a congenital heart disease are there any precautions i should take before going on long flights?

Depends on type: If you have a "cyanotic" congenital heart disease, you may need to wear oxygen during the flight. If your room air oxygen saturation (your doctor can check this) is <95%, you may need oxygen, and if <92%, you probably will.(managing passengers with respiratory disease planning air travel: bts recommendations. British thoracic society standards of care committee, thorax. 2002:57(4):289.).

DVT precautions: If your heart disease causes a problem with circulation in your legs, then you might want to consider wearing compression stockings to help prevent getting a deep vein thrombosis or a blood clot in your legs that can break off and cause real problems. This is definitely something to chat with your doctor about.