Dr. Robert Jarvik is best known for the artificial heart he pioneered more than a quarter-century ago. Since then he had toiled in relative obscurity — until he began appearing in television ads two years ago for the Pfizer cholesterol drug Lipitor.

The ads have depicted him, among other outdoorsy pursuits, rowing a one-man racing shell swiftly across a mountain lake. "When diet and exercise aren't enough, adding Lipitor significantly lowers cholesterol," Dr. Jarvik says in the ad...

Some of the questions may involve his credentials. Even though Dr. Jarvik holds a medical degree, for example, he is not a cardiologist and is not licensed to practice medicine. So what, critics ask, qualifies him to recommend Lipitor on television — even if, as he says in some of the ads, he takes the drug himself?