President Bush's irregular heartbeat is responding well to drugs and he can resume most normal activities, but strenuous exercise remains off-limits for the time being, his doctors said Monday.

Doctors at Bethesda Naval Hospital allowed Bush to return to the White House Monday morning after deciding against using an electrical shock procedure in an attempt to jolt his heart into a normal rhythm.Bush was rushed to the hospital Saturday afternoon after suffering shortness of breath and an accelerated heartbeat while jogging at Camp David, Md. The president was given two drugs, and his heartbeat stabilized for about six hours Sunday night but jumped back into an irregular rhythm at 4:45 a.m. Monday.

Shortly after Bush arrived at the White House at 9:45 a.m., tests showed his heartbeat had returned to normal, said Dr. Burton Lee, the president's physician.

"There's nothing more gratifying than working day and night on an arrhythmia and suddenly have it go well for you," Lee told a news conference in Bethesda.

Doctors recommended Bush resume normal activities except for his rather strenuous exercise regimen, which includes up to 45 minutes on a "Stairmaster" device.

The president has been told to "curtail exercise slightly" while his medicine is being adjusted, a process that may take a few days to a week, said Dr. Bruce Lloyd, chief of cardiology at Bethesda Naval Hospital.

"The man does a lot of conditioning," said Dr. Allan Ross, chief of cardiology at the George Washington University Medical Center. "For a few days we're going to try to hold him down a little bit. But he can be expected to live the same life he was living last week next week."

Doctors said they do not know what triggered the irregular heartbeat and were reluctant to blame exercise like jogging for the problem. They noted that when the president's heart reverted to the irregular beat early Monday, the problem occurred when he was sleeping.

Although Bush had complained of vague sense of feeling older while exercising in recent weeks, no signs of the heart problem were seen in Bush's physical in February, Lee said. "This came out of the blue," he said.

A battery of medical tests over the weekend found no problems with Bush's heart structure or any chemical imbalances that could account for the irregular heartbeat, the doctors said.

"We want to reiterate that this man really has no symptoms of any kind - no physical problem we can determine outside of this arrhythmia (irregular heartbeat)," Lee said.

Doctors considered using an electrical shock procedure called electrical cardioversion to get Bush's heart beating in a normal pattern. However, that option was rejected because Bush "had such a nice response to the drugs" and his condition could be monitored closely by medical staff at the White House, Lee said.

Lloyd said the fact that Bush was the president did not influence his decision to allow him to leave the hospital Monday and return to work. Some patients with similar symptoms are not even admitted to the hospital for treatment, he added.

In addition to the two drugs to combat arrhythmia, digoxin and procainamide, Bush is continuing his practice of taking one aspirin a day, which helps reduce the risk of heart attack by thinning the blood, doctors said.

Atrial fibrillation can boost the risk for strokes due to blood clots forming in the inefficiently pumping heart. But Bush's doctors said no sign of clots had been found and there was no need for any other anti-clotting agents.