The 95-year-old Oscar-winning actor, 64-year-old Arakawa, and one of their dogs were found dead on February 26 in separate rooms of their Santa Fe home.
Hackman's heart disease and the hantavirus pulmonary syndrome that caused Arakawa's death were announced at a press conference at the Santa Fe Sherriff's office on Friday in Santa Fe, New Mexico.
The sheriff told reporters last week that a pathologist determined the last signal from the actor's pacemaker was from February 17, making it likely that was the last day of the actor's life.
Hackman and Arakawa, a pianist, called Santa Fe home since the 1980s and were active in the city's art community and culinary scene. In recent years, the couple were seen less often in town as his health deteriorated. They lived a very private life before their deaths, Mendoza said.
A caretaker at their gated community discovered the couple dead. Sheriff's deputies found Hackman in the kitchen. Arakawa and a dog were found in a bathroom, with scattered pills from an open prescription bottle on the bathroom counter.
Both Hackman and Arakawa appeared to have suddenly fallen to the floor and neither showed signs of blunt force trauma.
One door was found ajar at the back of the house. Two of the couple's surviving dogs had used it to move in and out of the house, Mendoza said.
Hackman, a former Marine known for his raspy voice, appeared in more than 80 films, as well as on television and the stage during a lengthy career that started in the early 1960s.
He earned his first Oscar nomination for his breakout role as the brother of bank robber Clyde Barrow in 1967's Bonnie and Clyde.
He won an Oscar for best actor in 1972 for his portrayal of detective Popeye Doyle in The French Connection, and in 1993 won an Oscar for best supporting actor for Unforgiven.
