The title "Et In Arcadia Ego" is a quotation from Virgil's 'Eclogues'. It refers to the character of Death, and suggests that even in Paradise- Arcadia- there is no escape from Death. The translation from Latin is "I [Death], am also here in Arcadia.".
In artistic works, "Arcadia" symbolizes Utopia or Heaven; so the title translates from Latin as "I'm in Heaven" (the "I" being God).