Frances and Marlow Cowan are nonchalant that a video of them has gone viral on YouTube. Part of that is their laid-back Iowa demeanor, but mostly it's that they'd never heard of YouTube -- and they have no idea what "going viral" means.

Told that it means that a video of them playing a piano duet in the atrium of the Mayo Clinic has been watched more than 6.6 million times, Marlow Cowan replied: "Wow! People must not have much to do."

It all started when Marlow, 91, went to the Mayo Clinic for a physical. He and Frances, 85, spotted a piano in the atrium with a sign inviting people to play it. So they did.

The Cowans, who live in Ankeny, often entertain at hospitals, retirement homes and schools, so they were comfortable playing in public. "Every time we had a break between tests, we'd go down and play," Marlow Cowan said.

Crowds grew, and soon the Cowans started taking requests. Jodi Hume, who had taken her mother to the clinic, filmed them and put the video on YouTube.

"We're not into computers," Marlow said. "We started getting calls from people we'd never heard of saying that they'd seen us on YouTube. And we said: 'What's YouTube?'"

Eventually calls started coming from national media. The couple played on TV's "Good Morning America."

"They flew us out to New York," Marlow Cowan said. "Imagine: Traveling that far just to play the piano."

The Cowans, who traveled to Mayo last week and played an encore performance in the atrium, are taking their new-found celebrity in stride.

"We don't use words like 'celebrity' around here," Marlo Cowan said. "We don't think much about being famous. We just like to do what we do."