Sen. Ted Kennedy, the last of three brothers who changed the American political scene in the 1960s, had "a good night's sleep" at a Massachusetts hospital, after he suffered a seizure Saturday while at the Kennedy family compound in Hyannisport, Mass.
Kennedy, age 76, is being evaluated by doctors to determine the cause of the seizure, but results are not expected until Monday or Tuesday, a Kennedy source said.
Kennedy, D-Mass., who has served in the Senate since 1962, was taken by ambulance to a Cape Cod hospital in the morning and later flown to Massachusetts General Hospital in Boston by helicopter.
"Preliminary tests have determined that he has not suffered a stroke and is not in any immediate danger," Kennedy's physician Dr. Larry Ronan said Saturday evening. "He's resting comfortably, and watching the Red Sox game with his family.
Kennedy's wife, Victoria, was with him at the hospital, Kennedy family spokeswoman Stephanie Cutter said. Several other members of the senator's family visited him at the hospital, including his three children, Kara, Edward Jr. and Rep. Patrick Kennedy, Democrat of Rhode Island, niece Caroline Kennedy and nephew, former Rep. Joseph P. Kennedy, II.
He spent much of the afternoon watching sports on television: first the Boston Red Sox game, then the Boston Celtics' playoff game against the Cleveland Cavaliers. Kennedy went to Cape Cod Hospital Saturday "after feeling ill at his home" in Hyannisport, Cutter said.
"We got a 911 call at 8:19 a.m. this morning for a request for an ambulance," Lt. Bill Rex, a spokesperson for Hyannisport Fire and Rescue, confirmed to ABC News, Saturday. "We transferred one male to Cape Cod Hospital in Hyannis."
Kennedy's doctors in Boston were contacted, and it was decided he should be taken to Massachusetts General Hospital for further testing.
Rex also confirmed that an ambulance was later used to transport Kennedy to an airlift from Barnstable Municipal Airport for an emergency flight to Boston.
Kennedy is no stranger to brushes with death.
In 1964, only a year after the assassination of President John F. Kennedy, the newly elected senator and Sen. Birch Bayh, D-Ind., were nearly killed in a horrific plane crash that claimed the life of the pilot and one of Kennedy's aides.
Kennedy suffered two fractured ribs and three broken vertebrae in his back, an injury that would cause him a lifetime of back pain.
In October 2007, Kennedy had surgery to repair blockage in the left carotid artery in the neck believed to be connected to the injuries he suffered in the crash more than 40 years ago.
In July of 1969, a year after the assassination of his brother, Sen. Robert F. Kennedy, the senator once again escaped a fatal crash.
After a night of partying, Kennedy drove his mother's 1967 Oldsmobile over a wooden bridge on Chappaquiddick, an island off of Martha's Vineyard, killing passenger Mary Jo Kopechne.
Questions surrounding why Kennedy survived while Kopechne drowned have haunted the senator ever since.
He was convicted of leaving the scene of an accident and lost his license for a year, but the Kopechne family never sued the Kennedys or the senator for his role in the incident.
In more recent years, Kennedy was traveling with the late Sen. Paul Wellstone, D-Minn., on the day Wellstone's campaign plane crashed just outside of Eveleth, Minn.
Kennedy had been on several flights with Wellstone on the twin-engine turboprop but did not accompany him on the fatal flight as Wellstone was traveling to a funeral and not a campaign event.
Wellstone, his wife, daughter, three staffers and the two pilots were all killed in the crash.
The Cape Cod Times first reported this weekend's medical emergency and has posted a photo of Kennedy being taken to a MediFlight on a stretcher.
A Democratic Senate source told ABC News, "The situation is serious. We just don't know how serious."
The Kennedy family was set to host the annual Best Buddies Challenge event Saturday evening at the Kennedy family compound.
Even though he is the third-longest serving senator in the history of the body -- with 45 years and two months in office, behind only current Sen. Robert Byrd of West Virginia and Strom Thurmond of South Carolina -- Kennedy is one of the hardest-working members of Congress.
As the chair of the Health Education and Labor Committee, he was the Democrat who ran the Senate floor last week when senators were considering a bill to give collective bargaining rights to all police and firemen. He was also the chief Democrat who fought for a recently passed student loan improvements bill.
Kennedy chaired a widely covered hearing on May 12 about how to fight cancer. Among the people who testified during that hearing were Lance Armstrong, Elizabeth Edwards and Steve Case.
Kennedy was also set to play a pitvotal role for Democrats as they consider the supplemental war funding bill next week. Kennedy was one of the loudest critics of the war in Iraq from its outset.
Before his illness this weekend, Kennedy was apparently working; his office released a statement in his name, congratulating Benjamin Jealous on his election as head of the NAACP.
Kennedy and his brother Robert, who was a senator from New York, are the only two people to serve in the Senate at the same time as siblings.
Sen. Barack Obama, D-Ill., who received an endorsement from Kennedy and his niece Caroline Kennedy before the Super Tuesday contests in February, told reporters he has "been in contact with the [Kennedy] family."
"They are in our thoughts and prayers," Obama said. "As I have said many times before, Ted Kennedy is a giant in American political history. He has done more for health care of others than just about anybody in history, and so, we are going to be rooting for him. And I insist on being optimistic about how it's going to turn out."
Sen. John McCain, R-Ariz., the presumptive Republican presidential nominee, also released a statement on Kennedy, saying, "I was very sorry to hear that Sen. Kennedy has taken ill, and like millions of Americans, Cindy and I anxiously await word of his condition. Sen. Kennedy's role in the U.S. Senate cannot be overstated. He is a legendary lawmaker, and I have the highest respect for him."
Sen. Hillary Clinton, D-N.Y., campaigning in Oregon, said, "Our thoughts and prayers are with Ted Kennedy and his family today. We wish him well, and a quick recovery."
Sen. John Kerry, Massachusetts' other senator, who was at the hospital with Kennedy and other members of his family, released a statement saying, "Ted Kennedy is beloved and respected on both sides of the aisle in the Senate, in which he's been a giant for close to half a century, a legend in Massachusetts, and a dear friend to me and [Kerry's wife] Teresa.
"He's also been a fighter who has overcome adversity again and again with courage, grit and determination," Kerry's statement said. "Teresa and I are praying for Teddy, Vicki and all of his family, and we know that everyone in Massachusetts and people throughout the nation pray for a full and speedy recovery for a man whose life's work has touched millions upon millions of lives."
The Associated Press and ABC News' Dean Schabner, Eloise Harper, Bret Hovell, George Stephanopoulos and Sunlen Miller contributed to this report.