Arsenal fought back from 2-0 down with goals from Granit Xhaka and Olivier Giroud to go in level at half-time.
The hosts raced into a two-goal lead with a quickfire double from Jonathan Cafu and Claudiu Keseru, but on in the 20th minute Xhaka converted from Mesut Ozil's cross to reduce the arrears.
As an entertaining half drew to a close, Giroud headed home Aaron Ramsey's cross to level the scores.
Setting the Scene
Both teams had faced a long trip to get to the game, as Ludogorets' Razgrad home is some 350km from Sofia.