United States Supreme Court Justice Ruth Bader Ginsburg underwent unexpected heart surgery, a court spokesperson said Wednesday. The 81-year-old judge reportedly experienced discomfort while exercising with her personal trainer on Tuesday night.

Doctors at MedStar Washington Hospital Center discovered a blockage in Ginsburg’s right coronary artery, the Associated Press reports. A stent was inserted to clear the blockage. Ginsburg remained under observation and was resting at the hospital Wednesday, NBC News reports. Her release is expected within the next two days.

Citing concerns over her age and health, liberals have urged Ginsburg to resign from the Supreme Court for months, with some pushing for the resignation to occur ahead of the recent midterm elections. A resignation would allow President Barack Obama and his Democratic allies in Congress to nominate Ginsburg’s successor while they still have the power and votes to do so. It would be difficult to replace Ginsburg with a liberal justice if a conservative president succeeds Obama, they posited.

“That’s why I need a Democratic Senate,” Obama said in August, according to CNN. “Not to mention the fact that we’re going to have Supreme Court appointments, and there are going to be a whole host of issues that many people here care about that are going to be determined by whether or not Democrats retain the Senate.”

A White House official later clarified that Obama’s comments were not made in reference to a specific Supreme Court seat. And Ginsburg said in September that she had no plans to resign from her position.

“Who do you think President Obama could appoint at this very day, given the boundaries that we have? If I resign any time this year, he could not successfully appoint anyone I would like to see in the court,” Ginsburg told Elle magazine at the time. “[The Senate Republicans] took off the filibuster for lower federal court appointments, but it remains for this court. So anybody who thinks that if I step down, Obama could appoint someone like me, they’re misguided. As long as I can do the job full steam…. I think I’ll recognize when the time comes that I can’t any longer. But now I can.”

President Bill Clinton appointed Ginsburg to the Supreme Court in 1993. She was the second woman to be appointed to the court.