PHILADELPHIA (AP) _ Surviving Siamese twin Angela Lakeberg, who has already beaten the odds just by being alive, underwent a successful non-surgical procedure to widen her pulmonary artery.

Doctors at Children's Hospital of Philadelphia inserted a balloon catheter into a vein in Angela's leg and a stainless steel shunt to widen the artery pumping blood from her heart to her lungs.

The 7-month-old girl was listed in serious but stable condition this morning following Tuesday's three-hour procedure, said hospital spokeswoman Beatrice Parker.

''She's doing good. She's coming along,'' Parker said.

Angela and Amy Lakeberg were joined at the chest when they were born June 29, 1993, at the Loyola University Medical Center near Chicago. They shared a common heart and fused liver.

Amy died Aug. 20 during a 13-hour operation at Children's Hospital to separate the twins.

Because the two shared a single heart, it was known all along that Amy would not survive the operation. But Angela's chances were not considered much better, with some doctors saying before the operation that she had only a 1 in 100 chance of survival.

Doctors had known for months about Angela's arteriostenosis, or narrowing of the artery. They will be able to inflate the tiny shunt as Angela grows, said Dr. Elsa Suh.

Angela remains on a negative pressure mechanical ventilator, a device similar to an iron lung, to assist her breathing.

''It would be nice if people would pray for her,'' said Michael O'Dor of Portage, Ind., the brother of Angela's mother, Reitha Lakeberg.

The baby's father, Kenneth, is serving a prison sentence for violating probation.