Kara Kennedy, the daughter of Sen. Edward M. Kennedy, died Friday after a workout at a Washington-area health club. She was 51.

The cause was a heart attack, according to the Edward M. Kennedy Institute for the United States Senate in Boston, which announced the death.

Her brother Patrick J. Kennedy, a former Rhode Island congressman, told The Associated Press, "She's with Dad."

Their father died in August 2009 at the age of 77 after a battle with brain cancer. Her mother was Kennedy's first wife, Joan Bennett Kennedy.

In 2002, Kennedy received a diagnoses of lung cancer, and some of her doctors deemed it inoperable. But she found surgeons who were willing to treat her, and the cancer went into remission.

"Her magnificent strength in her successful battle with lung cancer was a quiet inspiration," the statement from the Kennedy Institute said, adding that she "provided her family and fellow patients with hope."

Patrick Kennedy told the AP that he thought his sister's cancer treatment "took quite a toll on her and weakened her physically."

She loved to exercise, he said, but "her heart gave out."