How is it possible i have heart failure at the age of 20 years old with no birth defects or heart problems from birth?

Depends on variables: Heart failure requires that it not keep up with the metabolic demands of the body by pumping nutrients around at an appropriate level for need. If your heart is injured by infection or otherwise (drug, injury) it would begin to fail. My first thought would be an infectious process.If the docs haven't found a reason they should keep looking.