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.
Hackman's wife died a week before he did, results showed. A reporter asked Sheriff Adan Mendoza if Hackman's advanced Alzheimer's had hindered him from perceiving her death.
"I would assume that is the case," Mendoza told reporters.
"He was in an advanced state of Alzheimer's and it is quite possible he was not aware she was deceased," Heather Jarrell, chief medical investigator at the New Mexico Office of the Medical Investigator, told reporters.
Arakawa is believed to have died around February 11, authorities said on Friday, citing the date of her last email.
Jarrell determined Hackman died on February 18, based on his pacemaker activity.
Hantavirus is a rare disease in the United States, with most cases concentrated in the western states of New Mexico, Arizona, Colorado and Utah. In northern New Mexico the virus is predominantly spread by droppings and urine of deer mice.
The virus is often transmitted through the air when people sweep out sheds or clean closets where mice have been living. It begins with flu-like symptoms and can lead to heart and lung failure, with around 38 to 50 per cent of cases resulting in death.
New Mexico has experienced between one and seven cases annually in recent years, according to health data.
State health inspectors found no particular sign of rodents inside Hackman's home but did detect rodent activity in structures outside the house, State Veterinarian Erin Phipps told reporters.
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.
Both Hackman and Arakawa appeared to have suddenly fallen to the floor and neither showed signs of blunt force trauma.
Arakawa had picked up one of her dogs in a crate on February 9 from a Santa Fe veterinarian, which may explain why the animal was found dead in the crate in the couple's home on February 26, Mendoza said. Phipps said the dog may have died of starvation.
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 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.
