Quick answers

What is Heidi in the Mountains about?

Heidi (1974) Japanese anime series by Zuiyo Eizo (now Nippon Animation) based on the Swiss novel Heidi's Years of Wandering and Learning by Johanna Spyri (1880). It was directed by Isao Takahata A feature-length film Heidi in the Mountains, aka The Story of Heidi, was edited from the series by Zuiyo (which by then was a separate entity from Nippon Animation, which employed many of the TV series' animation staff) distributed in 1979. All cast were replaced excluding Heidi and the grandfather. This movie is also the only incarnation of the Heidi anime to have been released commercially in the United States in English (on home video in the 1980s). Isao Takahata remarked "Neither Hayao Miyazaki nor I are completely related to any shortening version" on this work.

When was Heidi in the Mountains released?

Heidi in the Mountains was released on 6 January 1974.

Who made Heidi in the Mountains?

Heidi in the Mountains was directed by Isao Takahata.