NEW YORK — An autopsy of elite runner Ryan Shay was inconclusive Sunday after the 28-year-old collapsed and died in Central Park at the U.S. men’s marathon Olympic trials a day earlier.

“We want to take a closer look at the heart tissue,” said Ellen Borakove, spokeswoman for the city medical examiner’s office. She said the office likely would reach a conclusion in a week after examining Shay’s tissue on microscopic slides.

Shay collapsed about 51⁄2 miles into the race Saturday, and later was pronounced dead at a city hospital.

His father, Joe Shay, told The Associated Press on Saturday that Ryan was diagnosed with an enlarged heart at age 14. But doctors had repeatedly cleared him for competition, because having a larger than normal heart is not unusual among elite athletes. Training hard in aerobic sports, such as cycling, running or swimming, tends to result in a bigger heart that pumps more blood throughout the body.

Dr. Douglas Zipes, a spokesman for the American College of Cardiology who studies sudden deaths in athletes, said it can be difficult to differentiate a normal athlete’s heart from potentially deadly hypertrophic cardiomyopathy.

Cardiac echo tests and electrocardiograms can help evaluate whether the heart is healthy or not, said Zipes, a distinguished professor at the Indiana University School of Medicine. Genetic testing can also determine whether a person is at risk for certain problems.

Still, those precautions may not catch everything.

Joe Shay said doctors could not adequately test Ryan using a treadmill when he was a teenager because his heart rate was so low. Zipes said that’s not uncommon among elite athletes.

Shay’s wife, Alicia, also is a top distance runner. They married in July.

“My thoughts and prayers just go out to them and their family,” said winner Ryan Hall, a college teammate of Alicia’s at Stanford. “It’s a sad thing.”

Hall, Dathan Ritzenhein and Brian Sell won the three spots on the men’s marathon team, prevailing in a field of 131 that included Meb Keflezighi, silver medalist at the 2004 Olympics.

Hall, bellowing over the final mile with his victory ensured, had never run a marathon before April. But he served notice he could compete with the world’s best when he made the fastest marathon debut by an American, finishing eighth against an elite field in London in April.

On Saturday, he won in a trials record time of 2 hours, 9 minutes, 2 seconds. He was followed by Ritzenhein in 2:11:07 and Sell in 2:11:40.

Khalid Khannouchi, the 35-year-old former world-record-holder who has never made an Olympic team, was fourth, nearly a minute behind Sell. Khannouchi, who has battled injuries, could earn a spot on the squad if Ritzenhein later qualifies in the 10,000 meters and chooses to compete in that race instead in Beijing.