Sinatra, 82, was taken by ambulance from his Beverly Hills home to Cedars-Sinai Medical Center at 9 a.m. He was accompanied by his wife Barbara.
"Mr. Sinatra is at Cedars, where he is undergoing testing," his spokeswoman, Susan Reynolds, said. "In respect of Mr. Sinatra's personal request for privacy, there will be no further comment."
The ambulance traveled the eight miles to the hospital without lights and siren.
"It's a non-emergency. He's fine. He's here for tests," hospital spokeswoman Charlie Lahaie said.
Sinatra, who stayed overnight at Cedars-Sinai January 24 for a checkup, hasn't been seen in public since his heart attack in January 1997.
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