I dropped a heavy object on my finger and now it's completely blue. Do I need to seek medical attention?

The entire Finger or just the fingernail. If it's the entire finger. It wouldn't hurt to see a doctor. If its just the finger nail that's black... and you can still easily bend the finger back and forth, then its likely OK. Believe it or not I just did that myself yesterday but with a hammer. Yeah it does hurt... a lot.