DAVID LETTERMAN.

DAVID Letterman returns to his desk on CBS' "The Late Show" this Monday (Feb. 21), six weeks after he underwent quintuple bypass heart surgery. But is Dave crazy to get back into the ratings race so quickly?

UCLA cardiologist Dr. Jaime Moriguchi said it is not uncommon for bypass patients to return to work within four to six weeks, although it is encouraged that they take more time and join a rehab program.

Dr. Dan Schwartz, assistant professor of cardio and thoracic surgery at USC School of Medicine, said he would prefer patients like Letterman, who had his bypass Jan. 14, to wait another two weeks before returning to work.

Moriguchi, who treats bypass patients after their surgery, said it would take time for the bones in Letterman's chest to heal.

Psychologically, some bypass patients often become depressed post operatively, both doctors said. "The major thing after bypass surgery is not to deny what happened," Moriguchi said. "The plumbing works, but you have to work on reducing the risk factors."

Among new lifestyles Letterman has to adopt are changing his diet, exercising regularly, and using cholesterol-lowering drags. Letterman probably should quit smoking cigars or reduce the number he smokes. Both physicians said Letterman should avoid lifting heavy objects.

If these changes are not taken seriously, bypass patients can find themselves back under the knife because their arteries become clogged again. Moriguchi said Letterman's Type-A personality could work against him.

"Type As are workaholics, high stress, and don't want to sit around idly recovering at home," Moriguchi said. "They want to get back in the saddle, which is often why they develop (heart) problems to begin with."

One reason why Letterman may be rushing back to his late-night show is that CBS's ratings for his reruns are faring poorly against NBC's "Tonight Show" with Jay Leno. Three weeks of Letterman reruns on CBS averaged a 2.7 rating, compared to a 4.5 average for NBC's "Tonight Show." New shows are also running with guest hosts interviewing former Letterman guests, which are running about 10 percent higher than the reruns in the ratings, CBS said.