What really is the prognosis for John Fetterman, the Democratic Senate nominee from Pennsylvania who had a stroke on May 13?

The 52-year-old lieutenant governor of Pennsylvania clinched his party’s nomination just a few days later, setting up one of the most consequential Senate contests of the midterm elections. But urgent medical questions remain.

He was discharged from the hospital, his campaign said on Sunday, and Mr. Fetterman has said doctors assured him that he would make a complete recovery — but the campaign has not said when he will be able to return to campaigning.

“I am going to take the time I need now to rest and get to 100 percent so I can go full speed soon and flip this seat blue,” Mr. Fetterman said in a statement on Sunday, adding that he felt “great” but intended to “continue to rest and recover.”

With such an important race in the balance, one that could decide the Senate majority, the state of Mr. Fetterman’s health is of intense public interest. Yet, despite repeated requests, his campaign did not make him or his doctors available to discuss his stroke and his medical treatment.

And specialists in stroke, heart disease and electrophysiology said that some of the campaign’s public statements do not offer a sufficient explanation for Mr. Fetterman’s described diagnosis or the treatment they say he has received.

The stroke, he said in a statement released by his campaign, was caused by a blood clot. He said the clot was the result of atrial fibrillation, a condition in which the upper chambers of the heart beat chaotically and are out of sync with the lower chambers of the heart. The campaign said the clot was successfully removed by doctors at a nearby community hospital, Lancaster General Hospital.

On May 17, the day of the primary election, Mr. Fetterman had a pacemaker and a defibrillator implanted in his heart which, his press office said in a statement, “will help protect his heart and address the underlying cause of his stroke, atrial fibrillation (A-fib), by regulating his heart rate and rhythm.” His press office said he is expected to fully recover from his stroke.

Medical specialists asked questions about Mr. Fetterman’s treatment with a defibrillator. They say it would make sense only if he has a different condition that puts him at risk of sudden death, like cardiomyopathy — a weakened heart muscle. Such a heart condition may have caused the blood clot. Or, the doctors say the campaign could be correct about afib causing the clot.

Thrombectomy, the method likely used to remove the clot, also indicates that Mr. Fetterman experienced more than a tiny stroke, although prompt treatment may have averted damage and saved his brain.

“I was just in the hospital for over a week,” Mr. Fetterman said in a statement. “I am aware that this is serious, and I am taking my recovery seriously.”

In a brief interview on May 20, Gisele Barreto Fetterman, Mr. Fetterman’s wife, told the story of his stroke, from her perspective.

“We had been on the road campaigning,” she said. “We had had breakfast, and he was feeling fine.”

The couple got into a car to go to an event at Millersville University when, she said, “the left side of his mouth drooped for just a second.”

“I had a gut instinct that something was happening,” Ms. Fetterman said. “I yelled to the trooper, ‘I think he’s having a stroke.’ He said, ‘I’m fine. What are you talking about? I feel fine.’”

The state trooper soon drove Mr. Fetterman to Lancaster General Hospital where his treatment began. Ms. Fetterman said it involved going through his groin, which suggests he had a thrombectomy, a procedure in which doctors slide a small plastic tube through the groin, advance it into the brain and then pull the blood clot out using suction or a wire mesh.

It was not until two days later that his campaign reported that Mr. Fetterman had been hospitalized with a stroke. Asked about the delay, Ms. Fetterman said, “Less than 48 hours is pretty impressive timing when dealing with sensitive medical issues.”

Shortly after that question, Rebecca Katz, a senior adviser in Mr. Fetterman’s campaign, abruptly ended the call with Ms. Fetterman.

Medical specialists said that some aspects of the story were difficult to reconcile with their knowledge of stroke treatment.

Dr. Lee Schwamm, a stroke specialist at Massachusetts General Hospital and professor of neurology at Harvard Medical School, said doctors do a thrombectomy only when a large artery in the brain is blocked.

“You typically wouldn’t do it for someone with just a little bit of facial droop,” he said. Dr. Schwamm wondered if the doctors who examined Mr. Fetterman in the hospital had noticed other symptoms, like a loss of vision on his left side or lack of awareness of his left side, often called “neglect.”

“These strokes tend to be very severe,” Dr. Schwamm said. “He is fortunate that he went to a hospital that could treat it.”

Pressed about the stroke symptoms as described by Ms. Fetterman, a spokesman for Mr. Fetterman wrote in an email that he “told The Associated Press last week that Gisele ‘noticed that John was not himself, and shortly after he started slurring his speech.’”

But what caused the stroke?

Ms. Fetterman said her husband knew he had atrial fibrillation, which confers a high risk of stroke, and that he had taken anticoagulants, a standard method of reducing the stroke risk in people with atrial fibrillation, “on and off.”

But the treatment with a pacemaker and defibrillator is a puzzle if all he had was atrial fibrillation, medical specialists said.

“This doesn’t entirely make sense,” said Dr. Brahmajee Nallamothu, an interventional cardiologist at the University of Michigan.

Dr. Elaine Wan, an associate professor of medicine in cardiology and cardiac electrophysiology at Columbia University Medical Center, said defibrillators — which always come with pacemakers — are used to prevent sudden death. They usually are implanted in people with weakened heart muscle, or those who survived an episode in which the heart stopped, or in people with a genetic predisposition for sudden cardiac death.

“We would not use it for atrial fibrillation,” Dr. Wan said.

Dr. Rajat Deo, an associate professor of medicine and a cardiac electrophysiologist at the University of Pennsylvania’s Perelman School of Medicine, agreed about the use of defibrillators and said he shared Dr. Wan’s suspicion that Mr. Fetterman has a damaged heart.

“I think it would be fair to say he has at least two separate issues,” Dr. Deo said of Mr. Fetterman. “One is afib, from which he most likely suffered a stroke that was successfully treated.”

He added, “The second issue is that he likely has some underlying cardiac condition that increases his risk for ventricular arrhythmias and thus sudden cardiac death.”

The afib could be related to the other condition, Dr. Deo said. Patients with a weakened heart muscle are also at risk of developing atrial fibrillation.

On the other hand, Dr. Deo says, Mr. Fetterman’s atrial fibrillation may have nothing to do with his weakened heart. Without more information from his doctors it is impossible to know.

Dr. Deo added that if Mr. Fetterman is receiving appropriate state-of-the-art medical therapies and is protected with a defibrillator from sudden cardiac death, “he should do quite well while he continues his campaign.”

Experts also raised concerns about the prospects for former Vice President Dick Cheney, who had a defibrillator implanted in 2001. He finished two terms in the White House, including a hard-fought re-election in 2004.

And there is time before general election campaigning in Pennsylvania begins in earnest: It is unclear who Mr. Fetterman’s opponent will be, as the Republican race remains too close to call and may head to a recount.

But Dr. Wan was less sanguine than Dr. Deo about Mr. Fetterman.

“He is at risk for sudden cardiac death,” she said. “For someone on the campaign trail that might raise concerns.”