Doctors found a blood clot in Dick Cheney's left lower leg on Monday and have put the vice president on blood thinning medication to be taken for several months.

Cheney visited his doctor's office at George Washington University Medical Faculty Associates in the afternoon following mild calf discomfort, said spokeswoman Lea Anne McBride.

Cheney, 66, has previously been treated for a heart condition and has a pacemaker to regulate any irregular heartbeat. His annual physical in July showed his overall heart condition was stable. At the time, an electrocardiogram was also taken to check on repaired aneurysms on the back of his knees that were repaired through surgery in 2005.

Cheney has had four attacks; the first in 1978, when he was 37, and the fourth on Nov. 22, 2000, after the election that made George W. Bush president.

Cheney has been traveling a lot and air flight is frequently blamed for blood clots. He recently returned from Afghanistan and Pakistan.

Monday's ultrasound revealed a deep venous thrombosis or DVT. The vice president was not admitted to the hospital and has since returned to the White House to resume his schedule, McBride said.

"He'll maintain his regular schedule," McBride said. "He feels fine."

FOX News' Bret Baier and The Associated Press contributed to this report.