ARTIFICIAL valves inserted in babies' hearts to counteract a life-threatening defect are too small to handle the blood flow in an adult heart, according to a cardiac expert. The valves were inserted at Grantham Hospital in 50 babies between the mid-1970s and 1988 after they were born with their outgoing heart arteries transposed. Most now suffer irregular heartbeats or high blood pressure which could lead to sudden death. The hospital is seeking check-ups with all of them. The valves were too narrow to cope with the increase in blood flow rate as the baby grew to an adult, said a Prince of Wales Hospital cardiac anaesthetist and member of the Hong Kong Society of Critical Care Medicine. A baby's blood flowed at rates of up to 0.5 litres a minute, compared with an adult flow of 15 litres a minute. 'No engineer could design a heart with that degree of adaptability,' he said. 'By definition you have got a second-rate heart [despite the surgery].' The students would need life-long medication and should avoid exercise that would strain their hearts. But paediatric cardiologist Rita Sung Yn-tz said patients could live for years without noticing the problem. The rare condition afflicts up to 10 babies each year. In contrast, her 1993 survey of babies born at the hospital indicated that seven babies in every 1,000 was born with some sort of heart problem. And nearly all would lead healthy lives after operations in their first weeks of life. Last year, Hong Kong recorded 69,400 births, of which about 480 would have been born with heart defects. About a third of the babies had a hole in the heart, she said.