A necropsy performed on a Great Dane-labrador mix that died during a walk in Central Park apparently revealed that the dog had an enlarged heart.

The dog's owner, David Burke, had let Duke off-leash in Central Park, near 110th Street and Central Park West, around 11 p.m. (dogs are allowed off-leash in certain areas between 9 p.m. and 1 a.m.) when the 90-pound canine collapsed. When Burke caught up with him, the Post reports that he yelled "Are you okay? Are you okay?" and found Duke "convulsing" with a "single puncture wound to his skull, cops said."

Burke called his vet and then 911, reporting that Duke had been shot, but later said he did not hear gunshots. He also called his 15-year-old daughter, who was seen comforting her father and Duke.

"It looks like it may be natural causes,” a police source told the NY Times, adding that the puncture wounds to the dog’s head "appeared superficial and did not penetrate its skull."

According to one pet care website, "an enlarged heart in dogs develops when the heart’s muscles weaken, causing pressure in the heart’s blood vessels to increase and, in turn, stretching the muscles. Valvular defects, heartbeat abnormalities, tumors, and heartworms can all be behind the initial weakening of the muscles."

According to the Times, Duke had been abandoned on the side of the Moshulu Parkway in the Bronx and was 40 pounds when Burke saw him at a Manhattan animal shelter four years ago:

For Mr. Burke, it was the second tragedy in just a few days: On Saturday, his wife, Eileen, died at home from pancreatic cancer after being sick for three years. It was Eileen, he said, who had taken a particular liking to Duke at the pound.

“She fell in love with him at first sight,” Mr. Burke said.

The investigation into Duke's death is continuing, but the necropsy indicates that he had an enlarged heart. A police source told the Times, "It looks like it may be natural causes." The wound on his head "appeared superficial," and probably occurred when Duke fell.

Burke said that Duke was a "magnificent, gentle and intuitive animal."