Washington — Democratic presidential hopeful Bernie Sanders was declared to be in good health by his primary physician and fit for the presidency by two cardiologists after suffering a heart attack in early October.

Sanders, a senator from Vermont, released letters from the three doctors Monday, following through on his plan to disclose his health records by the end of the year.

Dr. Brian Monahan, the attending physician to Congress, said in one letter that Sanders, 78, is "in good health" and has been "engaging vigorously in the rigors of your campaign, travel, and other scheduled activities without any limitation."

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With a height of 6 feet and a weight of 174 pounds, Sanders has been treated over the years for gout, hypercholesterolemia, diverticulitis, hypothyroidism, laryngitis secondary to esophageal reflux, lumbar strain and complete removal of superficial skin lesions, Monahan wrote. The heart attack Sanders suffered in early October was his "most significant event" in terms of his recent health.

While Sanders was prescribed a blood thinner and beta blocker following the heart attack, he has since stopped taking the medications as he's recovered, Monahan said.

"Your heart muscle strength has improved," the physician wrote.

Sanders was sidelined for several days after suffering the heart attack on October 1 while campaigning in Las Vegas and was admitted to the hospital. Doctors discovered a blockage in one artery and inserted two stents. He was discharged from the hospital October 5 and returned home to Vermont to recover.

Records released by Sanders' campaign reveal the senator underwent a physical examination December 19 and a treadmill stress test with continuous EKG monitoring December 11. The latter test is "an important clinical tool to evaluate exercise capacity and predict outcomes in patients with a cardiac condition," according to a letter from Dr. Philip Ades, the director of cardiac rehabilitation at the University of Vermont Medical Center.

Ades said Sanders exercised "to a level that is approximately 50% higher than other men his age with a similar diagnosis."

"Mr. Sanders is more than fit enough to pursue vigorous activities and an occupation that requires stamina and an ability to handle a great deal of stress," he wrote.

Dr. Martin LeWinter, attending cardiologist at the University of Vermont Medical Center, wrote in a separate letter that Sanders suffered "modest heart muscle damage" but "has been doing very well since." His blood pressure and heart rate were described as being "in optimal ranges."

"At this point, I see no reason he cannot continue campaigning without limitation and, should he be elected, I am confident he has the mental and physical stamina to fully undertake the rigors of the presidency," LeWinter wrote.

At 78 years old, Sanders is the oldest candidate seeking the Democratic presidential nomination. Vice President Joe Biden is 77 and Massachusetts Senator Elizabeth Warren is 70. President Trump is 73.

Sanders and Biden have faced questions as to whether they are too old to seek the presidency, and Sanders' heart attack brought concerns over age to the forefront of the 2020 race.