Dr. William C. DeVries, the only surgeon in the country with government permission to implant artificial hearts, said yesterday that his success with William J. Schroeder, the second recipient of a mechanical heart, has "vindicated" his push to do such operations.

DeVries also predicted that snowballing interest in the artificial heart could "change the whole concept of American medicine."

In a videotaped interview released yesterday, a spirited and optimistic Schroeder told DeVries that the plastic-and-metal pump feels like an "old-time threshing machine" that he hopes will allow him to return home and "go fishing."

"I think the snowball's started and I don't think anybody can stop it now," DeVries, 40, said in a telephone interview. "It will accelerate. There are many thousands of people dying a day, many . . . at the point where they would be willing to take part in this."

"A success dispels critics and naysayers," added DeVries, who now has two artificial-heart implants to his credit.

The first, which occurred two years ago at the University of Utah, met with mixed reviews. Seattle dentist Barney B. Clark's complication-ridden, 112-day post-operative period raised questions about the quality of life with the device and the cost of implanting. The procedure is estimated to cost between $100,000 and $250,000.

While cautioning that success of the artificial heart will be determined only after many more implants, DeVries criticized as being in the "intellectual dark ages" those who question whether such experimental and costly procedures should be attempted.

"I felt that I've been vindicated when I saw the patient and knew that he was alive and going in the right direction," said DeVries of Schroeder, who received his heart Nov. 25 at Humana Heart Institute International in Louisville.

For his part, Schroeder, 52, showed how lively he is in a 10-minute interview videotaped at the Humana Hospital-Audubon Sunday night. Describing DeVries as his "good-old buddy, Bill," Schroeder said the surgery has given him a new lease on life. "I feel like I got about 10 years more right now," he said, compared with the few weeks of life that doctors had told him he had before the surgery.

Schroeder, from Jasper, Ind., told DeVries that he hopes to "be the same way as I was when I was 40 years old . . . . I really feel I can get out of here and go fishing, watch ball games."

Saying that he wished everybody could put their hands on his chest and feel his new heart, Schroeder rolled his hands in front of him to demonstrate that the device is "just like a threshing machine. The old-time threshing machine. And it's just a pumpin' like everything."

Schroeder's condition was upgraded from critical to serious yesterday, the eighth day after the implant operation. There were no signs of the infection that doctors fear in the seven to 10 days after major surgery.

In his interview with The Post, DeVries said he remains hesitant to make predictions about Schroeder, given the complications that befell Clark. But the doctor said "if things go well," Schroeder could be out of the hospital by Christmas. He would not return home, but would stay in Louisville for further monitoring.

In his Sunday interview, Schroeder was in good spirits, saying he felt "fantastic." His color was good and he spoke with a strong voice, frequently gesturing and at one point pulling out a breathing tube in his nose to show how well he could breathe on his own.

In contrast, Clark, in an interview with DeVries three months after his implant, was described as weak and short of breath. Clark died three weeks later.

"Dr. Clark was never really in the condition that Bill Schroeder is right now . . . ," DeVries said. "I never really doubted that we would do as well" with a healthier patient.

Clark, 61, was described as within minutes of death at the time of his implant, and had a history of kidney and lung problems that made recovery difficult. DeVries said Clark was a "perfect" first patient whose operation was a "success for humanity . . . . His goals were to help other people to live longer."

DeVries said that criticism about the quality-of-life issue was muted in part when a patient does so well so soon after surgery. On the videotape, Schroeder recalled he was "getting weaker and weaker" when he entered the hospital.

Since the surgery, DeVries said he has been visited by representatives of four other centers interested in doing similar operations.

He recalled that he had little financial backing before and after the Clark surgery and thought that the government had become a "dry well." When Humana Inc., which runs a profitable chain of hospitals, offered to back him and fund up to 100 implants, he said he decided it was "one of the only ways I was going to be able to do the project" about which he felt so strongly.

While DeVries believes that society must judge whether the benefits of the implant outweigh its costs, he argued that the debate is premature. "We have to find out if it works and then [debate]what it costs," he said.

Others have argued that once a new technology gets established, it is too late for a critical cost estimate. Clark's care cost $250,000, but Humana believes it may be able to cut that amount by half.

For now, DeVries is studying Schroeder's recovery, with an eye toward completing his first seven implants in the next year. He said he could be ready for his third patient "within weeks."

DeVries also said that Schroeder is now well enough to undergo some experiments to help researchers better understand the cardiovascular system.

DeVries said he already has begun tests to turn the mechanical heart up and down to see what effect this has on the body, and he said he soon will begin testing how cardiovascular drugs affect a patient with a mechanical heart.

Admitting that such experiments "pose additional risks," DeVries said he had Schroeder's permission and trust. "My primary goal is giving him a good quality of life," DeVries said.

DeVries said his most tender moment with his patient was when Schroeder was coming out of anesthesia -- "him reaching out and grabbing my hand and squeezing it." The taped interview with Schroeder showed the rapport between doctor and patient.

"We look forward to a long and productive time together," DeVries said. Schroeder responded, "You're super, doc." DeVries said, "You are, too.