The death of a three-year-old beluga at the Vancouver Aquarium last week was the result of heart failure, according to a necropsy that found a massive accumulation of fluid around Tiqa's heart and lungs.

Aquarium veterinarian Dr. Martin Haulena said the left side of the beluga's heart wasn't pumping blood away fast enough, which put pressure on the animal's lungs and led to the fluid buildup.

Haulena said the results of a number of tests are still pending, however, and a primary infectious cause has not been determined.

"There is a whole lot of information that still needs to come back and there are definitely puzzles that need to be solved," Haulena said, adding that the facility will leave "no stone unturned."

Some of the remaining tests may take months to complete. They include fatty acid signatures, tests for metabolic disorders, molecular techniques and endocrine, virology and toxicology tests.

The beluga was suffering from pneumonia as preliminary necropsy results indicated, Haulena said, but the cause is still being investigated. Pneumonia simply refers to an inflammation of the lungs, and can be due to infectious or non-infectious causes.

Tiqa was born on June 10, 2008, and died at around 5:45 a.m. on Sept. 16. About an hour earlier, a break-in was reported in the aquarium's beluga habitat, but police say there is no evidence suggesting the incidents are connected.

"The whale was not near that person as far as I know, so I'm not sure that there's a direct correlation there," Haulena said.

A number of human and veterinary experts from around the world are assisting the aquarium in investigating the beluga's death.

Dr. Stephen Raverty, a veterinary pathologist with the Ministry of Agriculture's animal health centre, said Friday that current results suggest Tiqa's death could not have been predicted or prevented.

Lesions in the beluga's heart and other organs indicate the whale's heart failure had been going on for some time, Raverty said. The cause could be congenital, related to toxins or the result of a yet-undetected virus.

Tiqa was the first calf in Canada to be born to an aquarium-born beluga. The beluga's death marks the second whale death at the aquarium in just over a year and the third death of a beluga calf in 10 years.

Nala died in June 2010 of a bizarre infection when a penny and two small stones became s tuck in her voice box.