nationality and heritage/bloodline are very different things. for example, my nationality is Canadian...but I am physically portuguese...which makes me portuguese blood...but of Canadian nationality. If i moved to France and stayed there and got my french citizenship, i then would have dual citizenship and can say i am of french nationality as well.
but when someone asks you "what ethnicity are you?" or "what are you?" you say your bloodline..because that is what makes you. but when they ask which nationality you are, you say where you reside and what society you've been living in.
anyway, that is the correct distinction. therefore, if you have a child in italy and you are american, and you return to america to raise that child, that child is american. but the child has dual citizenship because he/she was born in italy..but the majority of ppl would say they are american regardless of where they were born if they spent most of their life in america.
so there u go...difference between heritage and nationality.