It may well prove to be the most expensive musical instrument in the world — a Stradivari viola, whose asking price will start at $45 million when it is offered for sale this spring — but, just for a moment, it was held up with no hands.

The viola was tucked firmly under the chin of the violist David Aaron Carpenter, who briefly needed both hands to adjust his bow, which had frayed a little during a virtuosic run-through of Albéniz’s “Asturias” at a demonstration of the instrument arranged by Sotheby’s.

“I won’t go that crazy on this again,” Mr. Carpenter said with a smile after trying out the viola in an empty showroom at Sotheby’s, which plans to announce its sale on Wednesday. “It’s possibly the most expensive instrument in history, and I don’t want to break it.”

If the viola fetches anything near its asking price, it will dwarf previous sales records for musical instruments. The “Lady Blunt” Stradivari violin set an auction record when it was sold in 2011 for $15.9 million. While some instruments may have been sold privately for more, none are believed to have gone for anything near the $45 million being sought for this viola, which was owned and played by Peter Schidlof of the Amadeus Quartet until his death in 1987 in England.