Frankenstein Conquers the World (movie, 1965)

During WWII, Germans obtain the immortal heart of Frankenstein's monster and transport it to Japan to prevent it being seized by the Allies. Kept in a Hiroshima laboratory, it is seeming lost when the United States destroys the city with the atomic bomb. Years later a wild boy is discovered wandering the streets of the city alone, born of the immortal heart.