Pennsylvania Lt. Gov. John Fetterman (D) said Friday he needs "some more time" to recover from a stroke he suffered last month before he returns to actively campaigning for the state's open U.S. Senate seat and revealed he had ignored a heart condition.

Why it matters: Some state and national Democrats are worried about his absence from the trail, and he gave no solid timeline on when he may be able to return to campaigning in one of the most contested races in the country this midterm election cycle.

• Fetterman suffered a stroke just days before Pennsylvania's primary elections, in which he won the Democratic nomination for the Senate seat.
• After the stroke, he had a standard procedure to implant a pacemaker with a defibrillator.

Fetterman said that in 2017 he was diagnosed with atrial fibrillation, an irregular heart rhythm and a decreased heart pump, and he did not take care of himself after that diagnosis. He said his doctors told him that had he kept "taking the blood thinners, I never would have had a stroke."

What they're saying: “Doctors have told me I need to continue to rest, eat healthy, exercise, and focus on my recovery, and that’s exactly what I’m doing," Fetterman said in a statement Friday.

• "It will take some more time to get back on the campaign trail like I was in the lead-up to the primary. It’s frustrating – all the more so because this is my own fault – but bear with me, I need a little more time. I’m not quite back to 100% yet, but I’m getting closer every day," he added.
• “It’s not something I’m proud of, but it is something I hope that others can learn from," he added. "I didn’t do what the doctor told me. But I won’t make that mistake again."
• “This race is so important for Pennsylvania and for the country. I’m going to be ready for it, and I can’t wait to get back on the trail.”

He also released a letter from his cardiologist, Ramesh Chandra, who said "The prognosis I can for John's heart is this: If he takes his medications, eats healthy, and exercises, he'll be fine."

• "If he does what I've told him to do, and I do believe that he is taking his recovery and health very seriously this time, he should be able to campaign and serve in the U.S. Senate without a problem," the doctor added.

The big picture: It's currently unclear which Republican Fetterman will face in the election this fall, as the GOP primary between Mehmet Oz and David McCormick for the seat is still too close to call and is locked in a recount.

• An unnamed elected Pennsylvania Democrat told NBC News earlier this week that “A lot of us Democratic Party types are very nervous about" Fetterman's health.

Go deeper: What's the holdup in Pennsylvania's GOP Senate race?