Placing stents in arteries is a common procedure, and patients generally return home within a day or two. Ms. Sanders did not specify whether Mr. Sanders, 78, would be discharged sooner than the weekend and would remain in Las Vegas before returning home.

Dr. Brahmajee Nallamothu, an interventional cardiologist at the University of Michigan, said it is hard to read too much into Mr. Sanders’s apparently prolonged hospital stay. If a blood vessel’s anatomy is complex, he said, cardiologists might keep a patient for an extra day. But a stay of several days, he said, “is not typical unless there is an additional issue.”

Dr. Nallamothu said he had watched a video of Mr. Sanders’s event at a Las Vegas restaurant Tuesday night when the senator, looking distressed, removed his jacket and asked for a chair so he could sit down. The symptoms, Dr. Nallamothu said, suggest that Mr. Sanders might have had a small heart attack — defined as a blockage that results in some damage to the heart muscle — or almost had a small heart attack. But he does not seem to have had a major one.

With a smaller heart attack, a blood vessel is mostly blocked but a trickle of blood can still get through. If the person is sitting still, that can be enough blood to relieve symptoms. But if the person is standing and moving around — as Mr. Sanders was originally— the paucity of blood can cause chest pain and discomfort.

In her statement, Ms. Sanders, who traveled on Wednesday to Las Vegas and is now with Mr. Sanders as he recovers, said her husband was in a buoyant mood, that doctors were “pleased” with Mr. Sanders’s progress and that he had not needed any additional procedures.