Former President Gerald Ford (93) has been admitted to a California hospital for medical tests.
"President Gerald Ford has been admitted to Eisenhower Medical Center in Rancho Mirage, California, for medical tests. He is doing well," his spokeswoman said.
It was the fourth spell in hospital this year for Ford - the oldest living US president - who underwent heart surgery in August.
Mr Ford had an angioplasty procedure at the Mayo Clinic in Rochester, Minnesota, to increase blood flow through two coronary arteries and was fitted with a pacemaker.
In July, he was taken to a Colorado hospital after suffering shortness of breath, and in January he spent about 10 days in a California hospital with pneumonia.
Mr Ford took office in 1974 after Richard Nixon resigned amid the Watergate scandal. He lost his own bid for a four-year term to Democratic nominee Jimmy Carter in the 1976 presidential election.