The woman, whose name was not released, was in stable condition at University Medical Center in Las Vegas after losing her grip while performing at least 15 feet (4.6 meters) above the stage on a long white ribbon-like drape, said Anita Nelving, spokeswoman for Cirque du Soleil.
"She did slip and fall," Nelving said.
As she fell, the woman hit a second cast member who was knocked from the "aerial silk" drape and fell a short distance to the stage during the Tuesday night mishap. He was treated for minor injuries and released, Nelving said.
Audience members gasped when the two performers landed with a thud near the end of the 7:30 p.m. performance, the Las Vegas Review-Journal reported Thursday.
The show concluded shortly afterward, but many in the audience left. Some received ticket refunds, Nelving said.
The injured woman has been with the show for about six months, Nelving said. The man, 25, is from Brazil and has been part of the show since it began in September 2002.
The "aerial silk" act has been suspended for a safety review, Nelving said. She said two performers also fell while rehearsing the same segment in early 2006. A female performer injured in that mishap did not return to the act.
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969