Maniac (1934)

Don Maxwell is an ex-vaudeville ham wanted by police, who has somehow become the unlikely assistant to Dr. Meirschultz, a mad scientist in the business of reanimating corpses. Maxwell's gift of impersonation gets him and Meirschultz past the guards and into a morgue where they use a special serum to revive the corpse of a pretty young woman. But that's nothing. Dr. Meirschultz has a heart beating in a jar of solution and is eager to put it into a corpse that really needs it. Meirschultz gives his assistant a gun and advises him to commit suicide so that he can put the heart in him, but Maxwell shoots and kills the scientist instead and hides the body. People will miss Meirschultz, Maxwell quickly realizes, but no one will miss his lowly assistant; so Maxwell dons eyeglasses and a fake beard to become his onetime benefactor. The trouble is, he impersonates the mad doctor too well and goes crazy himself.