The Reservoir Dogs actor was found dead at his home in Malibu, California, at the age of 67 last week, and his cardiologist has now confirmed the cause of his passing.
The unnamed doctor told NBC4 Los Angeles that heart failure will be listed as the cause of death, with heart disease and alcoholism named as contributing factors.
An autopsy will not be conducted because the Kill Bill star's cardiologist signed the death certificate, and the Los Angeles Sheriff's Department has closed its investigation into Madsen's death and listed it as being due to natural causes.
Madsen was found unresponsive in the early hours of Thursday when deputies responded to his home after a 911 call and he was pronounced dead at the scene.
The Hateful 8 star's manager Ron Smith told Dailymail.com that he died from a "cardiac arrest".
"In the last two years Michael Madsen has been doing some incredible work with independent film including upcoming feature films Resurrection Road, Concessions and Cookbook for Southern Housewives, and was really looking forward to this next chapter in his life," his representatives said in a statement.
"Madsen was also preparing to release a new book called Tears For My Father: Outlaw Thoughts and Poems.
"Michael Madsen was one of Hollywood's most iconic actors, who will be missed by many."
The actor suffered heartbreak in 2022 when his son Hudson took his own life at the age of 26.
The star is survived by his five other children and wife DeAnna Morgan.
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