In a phone interview on "Fox & Friends" with hosts Steve Doocy, Ainsley Earhardt, and Brian Kilmeade, the president insisted it was part of his yearly physical.
Fox News had previously reported that the president spent more than two hours at the medical center on Saturday. The appointment -- which followed a previous exam in February -- didn't appear on the president's public schedule, as was the case for his physicals last year and this year.
The president told the "Friends" hosts that his doctor called him and asked if he would "like to do" the "first part" of his physical at that time.
"Because I'm going to be slightly busy in 2020 in January and February," he explained. "Especially if 'Crazy Nancy' does something that nobody ever would even think of doing. So, I'll be busy interviewing Biden, watching the interviews of 'Shifty Schiff' and why he had made up all of this stuff and why he made up my statements."
The president said, "Yeah. Go ahead. Let's go."
"So, we drive out to Walter Reed. Greatest doctors. Greatest everything. Greatest place you've ever seen what they can do," said Trump.
He said that, in addition to receiving the first part of his physical, he met with parents and families, including the wife of a young soldier who had lost an arm and a leg. He also took a "little tour" of the building.
The president later tweeted about his visit.
"Everything very good (great!)," the president wrote. "Will complete next year."
"On the way back I'm hearing rumors that I'm in the hospital. Then I'm hearing rumors that I had chest pains. Then I'm hearing rumors that I had a massive heart attack. Then I'm hearing rumors that I'm not coming back. I'm staying at Walter Reed overnight and maybe for a long time," he said incredulously.
"I come home and my wife says, 'Darling! Darling! Are you OK?' I say. 'OK from what?'" he recalled. "CNN. Mostly CNN, but that stupid MSNBC, which is just as bad. Can you imagine? I made them so much money on 'The Apprentice.' But, anyway, those two. And so, they started a false narrative. And, it was this."
"No matter what we told them, they were going with it," he exclaimed. "It's so disgusting what they do because they knew it wasn't true. They went with it."
Trump's visit led to immediate media speculation that something was amiss. On CNN, Barack Obama's former physician claimed Trump may have "neurological issues" while Dr. Sanjay Gupta also questioned whether the White House was telling the truth.
Fox News' Vandana Rambaran and The Associated Press contributed to this report.