As you mentioned you are suffering from congenital heart diseases.
So antibiotic cover is a must prior to any dental procedure to undertake.
ItS better not to get tattooing as chance of developing infection is very high.
administered prior to tattooing can prevent occurence of infective endocarditis
,you must get a consent from your cardiologist before getting it done.
Also be very conscious about your dental health.
Maintain good oral hygiene
Take a balanced diet and routine exercises has to be done.
Hope this helps.