Baby Kaylee suffers from a rare brain abnormality that could cause her to stop breathing. (Family photo/Canadian Press)

Baby Kaylee, who made headlines in April when her parents offered to donate the then critically ill infant's heart to another baby girl, is back in Toronto's Hospital for Sick Children and on life support.

A spokesman for the family says the baby, who is from from Bradford, Ont., stopped breathing Wednesday night, and her family couldn't revive her.

Paramedics rushed her by police escort to Southlake Regional Health Centre in Newmarket, Ont., and she was immediately transported to Toronto.

The four-month-old suffers from Joubert syndrome, a rare malformation of the brain and brain stem accompanied by interrupted breathing.

Spokesman J.P. Pampena says the family reports Kaylee might have suffered a heart attack or stroke, and doctors tell them she is now in critical but stable condition.

It is the second time Kaylee has returned to the hospital since being discharged in April. She was brought to the hospital at the end of May after contracting an infection.

When Kaylee was initially at the Hospital for Sick Children in April, she was expected to be taken off the respirator she needed to breathe. Doctors predicted she wouldn't survive more than 30 minutes once the breathing apparatus was removed, and her parents, Jason Wallace and Crystal Vitelli, decided to donate her heart to a baby girl from P.E.I. who was in the hospital and needed a heart transplant.

To her doctors' and parents' surprise, Kaylee rallied and was able to breathe on her own once being taken off the respirator and returned home to Bradford.