The most recent victim was Sunshine, a 34-year-old western lowland gorilla, who died Tuesday in the Detroit Zoo after suffering from heart disease for several years.

Cardiovascular disease is the leading cause of death in captive gorillas, the zoo said in a release. More than 40 percent of adult gorilla deaths are due to heart disease, The Washington Post (NYSE:WPO) reported Friday.

Scientists said they don't know why gorillas contract the disease at such a high rate. Possibilities include diet, disease, old age or some other unknown cause.

Veterinarian Suzan Murray said heart disease in gorillas is different from heart disease in humans. Gorillas develop a hardening of the heart muscle, called fibrosing cardiomyopathy, that has few symptoms, the newspaper said.