Heart co-founder and producer Micheal Fisher has passed according to his brother Roger:

Inducted in the Rock And Roll Hall Of Fame in 2013, Heart had originally been founded as The Army in 1967 by brothers Michael and Roger Fisher and Steve Fossen, evolving into Hocus Pocus for a few weeks in 1969 and then White Heart from 1970 to 1973, when vocalist Ann Wilson joined.
By 1973, the band name was shortened to Heart and by 1974, guitarist and vocalist Nancy Wilson had joined the band, who had begun writing for their debut album, Dreamboat Annie, a Multi-platinum album that was produced and engineered by the brothers and producer Mike Flicker at Mushroom Studios in Vancouver in the summer of 1975.
With the success of this album, Michael “Magic Man” Fisher decided to forgo his management of the band and instead decided to co-produce several of the band’s subsequent albums with Mike Flicker, including 1977’s Little Queen and 1978’s Dog & Butterfly, which were two more hit albums featuring his brother Roger.
I was a child in the 70’s and only encountered their recordings from time to time on the local radio stations. But I do remember liking them as a pre-teen and had begun collecting their recordings by my mid teens, starting with the band’s Greatest Hit Live album and self titled album on cassette.
I highly recommend their official biography, Kicking and Dreaming: A Story of Heart, Soul and Rock & Roll, which was a New York Times Bestseller in late 2012.