LITTLE ROCK (AP) -- An 8-year-old boy from Mexico received a new heart Monday to replace his diseased one, after spending weeks in a Texas intensive care unit and getting a rare implanted heart pump in Arkansas.

Adrian Saucedo went into surgery just after 3 a.m. for a procedure that lasted about seven hours, said Dr. Elizabeth Frazier, head of the cardiac transplantation program at Arkansas Children's Hospital.

His new heart, flown into Little Rock by an accompanying physician, began beating after warming inside the boy's chest, requiring no electrical shock to come back to life, Frazier said.

"It's always a miracle," Frazier told reporters at a news conference Monday afternoon. "Every time it happens, it's a miracle."

Frazier said Adrian would remain on a ventilator for about a day, then would have the tube removed from his throat so he could speak. Within four to five days, the doctor said Adrian would be up and moving around, a vast improvement for a boy who only weeks earlier needed an experimental heart pump implanted in his chest for him to continue living.

Adrian lives with his mother and father in Piedras Negras, Mexico, just across the border from Eagle Pass, Texas. He spent more than 60 days at Methodist Children's Hospital of South Texas, after doctors determined he suffered from cardiomyopathy -- a condition caused in his case by a viral infection eating away at his heart tissue.

While several hospitals rejected him as a transplant patient, residents of San Antonio, Texas, raised half a million dollars for the boy's treatment. Arkansas Children's Hospital in Little Rock admitted Adrian on April 19.

But within days of his arrival, Adrian's condition worsened. Doctors implanted a Berlin heart, the only blood pump available for children at risk of heart failure -- a rarity as the U.S. Food and Drug Administration only allows it in the most extreme circumstances.

Frazier said the hospital received word Sunday a heart matching Adrian's blood type and weight was available. Frazier said privacy rules prohibited her from saying where the heart came from. However, she said Dr. Robert D.B. "Jake" Jaquiss, the hospital's chief of pediatric cardiothoracic surgery, flew on a jet to retrieve the heart and bring it back to Little Rock.

The boy went into surgery with Dr. Michiaki Imamura and the hospital's heart team, even before the jet carrying the heart landed, she said.

"Fortunately, the donor heart in this situation promptly started once it warmed up," Frazier said. "It seems to be functioning well within the parameters we look at, but the first 24 to 48 hours is critical. Once things stabilize and his medications are stabilized, then we would hope that he would make progress as far as getting off of the breathing machine."

Currently, the boy and his family are in the United States on a humanitarian visa, and they plan to return home. Frazier said doctors at the hospital spoke with Mexican physicians about the care Adrian would need.

While Adrian's hospital care likely will exceed the half a million dollars raised for him, Frazier said the hospital would handle the rest of the finances without offering specifics. An official from Little Rock's Mexican consulate also attended the news conference.

Frazier said Adrian's chances at a full recovery were good -- 75 percent of all children who have heart transplants survive with chances even better for those who suffer the disease Adrian had. But the boy could face infection from the operation or kidney damage from being on the bypass machine.

"We're not out of the woods 'til we're out of the woods," Frazier said. "There's always that question in that once you transport a heart is it going to restart and how good is it going to feel about it. We've passed that hurdle."

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