The book 'Heath: A Family's Tale' says that the disease might be genetic as the late actor's uncle Haydn was recently diagnosed with the Bipolar disorder, a category of mood disorders.
Heath, who died due to accidental overdose of prescription drug, might have had swings between euphoria and despair due to the same disorder, according to the biography by Janet Fife-Yeomans.
"I don't mind people knowing I have bipolar disorder and it's a shame that it took this long to be diagnosed," News Of The world quoted uncle Haydn as telling the author.
The condition can be linked to traumas such as failed relationships.
Heath was devastated by his split last year with long-term love Michelle Williams, his Brokeback Mountain co-star and mother of their daughter Matilda.