Encouraged by Williams' progress since the surgery, doctors removed the pump and have been giving the 82-year-old Hall of Famer fewer medications, The Boston Globe reported Saturday.
But Williams, baseball's last .400 hitter, is still on a ventilator, attached to three IV lines and heavily sedated.
"The cardiac recovery is not yet complete, but he clearly is moving in the right direction," said Jeffery Borer, the cardiologist treating Williams. "I can say that with greater confidence today than two days ago."
Williams is expected to remain in New York Presbyterian Hospital's Weill Cornell Medical Center for several more days.
Monday's procedure was unusually long because of excessive bleeding caused by medication Williams had been taking, surgeons said. During the surgery a team of 14 doctors and nurses repaired the leaking valve with pig tissue.
Doctors also took longer than normal to stabilize Williams' heart after the surgery.
"It took several hours in the OR to deal with creating the optimal support system for him," Borer said.
After the surgery doctors were encouraged by Williams' response to commands, when he was asked to squeeze a doctor's finger.
Doctors said Williams' heart has been pumping more blood since the surgery and made the decision to remove the artificial pump Thursday. They are also satisfied with decreasing blood pressure in his lungs and say his kidneys and other organs are functioning well.
"We're entering a time now in which our concerns shift a little bit from the heart," Borer said. "He's been on a respirator now for five days and we must be extremely vigilant that he doesn't develop pneumonia. There are no signs of that yet, but we're watching constantly."
Doctors hope to remove the ventilator and the IV lines over the weekend. They also want to reduce the amount of heart drugs Williams has been given since the surgery.
Williams had a pacemaker inserted in November, but continued to suffer from shortness of breath, caused by the leaky heart valve.
Last Thursday, he entered a Florida hospital with what cardiologist Rick Kerensky described as "deterioration of his cardiovascular and neurological status." He was transferred to New York on Sunday.
Williams hit .406 in 1941 and had 521 career home runs, including a farewell homer in his last at-bat in 1960.
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