The 40-year-old Illinois woman who died after experiencing problems in the swim portion of the Nautica New York City Triathlon had suffered a cardiac arrhythmia.
Amy Martich died in August. The city Medical Examiner's Office said Monday that the arrhythmia was caused by a mitral valve prolapse. That's when a valve in the heart doesn't close properly.
Martich was one of two people who died after having problems in the race. A 64-year-old New Jersey man also died after being pulled unconscious out of the Hudson River.
The deaths were the second and third ones connected to the event in the last three years.
Participants in the yearly race swim about a mile, bike 25 miles and run 6 miles.