Whisper of the Heart was based on the manga Mimi o Sumaseba which was originally created by Aoi Hiiragi. The manga was serialized in Shueisha's shōjo manga magazine Ribon between August and November 1989, and a single tankōbon volume was released on February 20, 1990. The volume was reprinted on July 15, 2005.[3] A second manga by the same author titled Mimi o Sumaseba: Shiawase na Jikan was serialized in Shueisha's Ribon Original in August 1999 and released in a single volume on February 20, 1996. A spiritual sequel to this film adaption, The Cat Returns, was turned back into a manga by Aoi Hiiragi, under the name Baron: Neko no Danshaku.
During production, the backgrounds in the fantasy sequences of the film were drawn by Naohisa Inoue and the woodcut of the imprisoned violin-maker was created by Miyazaki's son Keisuke Miyazaki, a professional engraver.[4] Japanese musical duo Chage and Aska's short music video, titled "On Your Mark", by Studio Ghibli was released along with Whisper of the Heart.