"I must confess, I was dumb," the 2020 presidential candidate said outside his home in Burlington, Vt. "Thank God, I have a lot of energy during this campaign. I've been doing, in some cases, three or four rallies a day, going all over the state, Iowa, New Hampshire, wherever. And yet I, in the last month or two, just was more fatigued than I usually have been."
"I should have listened to those symptoms," the 78-year-old presidential hopeful said.
Sanders revealed that he never had a doctor in his Vermont hometown, "let alone a cardiologist," because his primary physician is based in Washington, D.C.
"We're going to meet him," Sanders said moments before getting in a car with his wife, Jane, to attend the appointment with his new physician. "I understand he's a very good cardiologist. Going to see him on a regular basis to get some checkups, and obviously, I'll be on-and-off in Vermont and so we're going to meet him today."
Sanders insisted he was "feeling good," adding that he doesn't think the heart attack, for which he had two stents inserted into his chest to help with blood flow, "helps or hurts" his chances of beating President Trump in 2020.
His campaign also downplayed any skepticism that his ailments would have a negative impact on his presidential run.
"Make no mistake, Sen. Bernie Sanders is as committed — more so, even more now than he always has been, if that's even possible," national campaign co-chair Nina Turner told the Associated Press in an interview.
Sanders is scheduled to attend the fourth Democratic presidential debate in Ohio next week. He said Tuesday that he "certainly intends to be actively campaigning" but will "change the nature" and frequency of rallies and events to "make sure I have the strength to do what I have to do."
“We were doing, you know, in some cases five or six meetings a day, three or four rallies and town meetings and meeting with groups of people,” Sanders said about his campaign prior to his heart attack. “I don’t think I’m going to do that.”
Even before Sanders was rushed to the hospital after complaints of chest pains during a campaign rally in Nevada last week, the candidate faced questions about his age. The 78-year-old is the oldest candidate in the race and would be the oldest person to be elected president, should he win.
Sanders said he still plans to release his medical records, promising to do so "at the appropriate time."
A spokesperson for Sanders did not respond to Fox News' request for comment.
"If there's any message that I hope we can get out there, is that I want people to pay attention to their symptoms," Sanders said. "When you're hurting, when you're fatigued, when you have pain in your chest, listen to it."
Sanders received another piece of bad news on Tuesday. His daughter-in-law, 46-year-old Rainè Riggs, died at a Pennsylvania hospital two days after being diagnosed with cancer, according to an obituary posted on the Lee & Martin Funeral Home Facebook page.
Riggs was married to Sanders' son Levi and the couple has three children.
The Associated Press contributed to this report.