There are many times in life when a do-over can come in handy. Perhaps you clicked “Send” on an email that was better left unsaid, or “Delete” on a contact before realizing you still needed it.

Your contacts will be restored to exactly the same state they were in at that time — any contacts that didn’t exist then will be deleted and any that have since been added will be deleted. You can always undo this change by restoring again if you didn’t get the time right.

Source : The Official Gmail Blog