The 53-year-old was taken to hospital after suffering chest pains while out paddle-boarding with his wife Camille, 39.
Publicist Stan Rosenfield confirmed that the actor, who lives in Hawaii, was recovering in a local hospital.
He is expected to be discharged later this week.
Kelsey played psychiatrist Dr Frasier Crane for 20 years on TV show Cheers and his own spin-off series, Frasier.
His heart scare comes 3 weeks after his latest US sitcom, Back to You, was axed. The series, in which he starred as a womanising TV news host, lasted just 1 season.