accidently used dd on the wrong drive

i was trying to make a bootable usb with disk dump command in ubuntu, but i typed the wrong device name and hit enter so it started the process on my external hard drive , but after a few seconds i realized i just did something retarded that i just destroyed my ex hdd which i used for important files and i cancelled the dd with ctrl+c,now my hdd is empty , and when i try to use it on my windows it asks to be formatted , how can i get my files back ?