Zoo: Cardiac problems killed dolphin

City zoo officials have determined that its 24-year-old Atlantic bottlenose dolphin died from cardiac problems.

Phoenix, a female dolphin, died June 24 of a problem similar to a heart attack, said zoo senior veterinarian Dr. Jeff Proudfoot.

Possible risk factors for the problem are similar to those of humans: genetics, infections, viruses or circulatory problems.

"We just don't know at this point exactly why this happened," Proudfoot said Wednesday in a statement by the zoo, "but we're going to go back and do some good science and try to understand this disease process more clearly."

Phoenix had behaved and eaten normally before her death, and had a physical examination in May that did not indicate any problems, zoo officials have said.

Dolphins in captivity typically live more than 25 years.