In the study, Dr. Adrian Dancea of The Montreal Children's Hospital and colleagues reviewed 848 autopsy records of infants and young children who died suddenly and unexpectedly in Quebec between 1987 and 1999.

The researchers found that 82 of the children had some sort of heart problem, representing 10% of the total number of sudden infant deaths, the authors report in the September issue of The Journal of Pediatrics.

In about half of the 82 cases, a structural defect of the heart was found. The remaining children had structurally normal hearts but some other heart condition.

"We found that heart disease is present in a significant percentage of autopsies of infants dying suddenly and unexpectedly," write the authors.

Dancea and colleagues note that structural heart problems are often picked up in the first few weeks of life. However, half of the SIDS infants with a specific type of malformation were not diagnosed with the problem before they died.

Most autopsies were performed by a pediatric pathologist, according to the report. However, if the autopsy was performed outside a pediatric center, a close examination of the heart's anatomy was not performed in a third of cases.

This suggests, according to the researchers, that heart problems may be underreported in cases of SIDS.

Dancea's team has "shown that a significant number of unexpected deaths in the young are the result of cardiovascular diseases, some of which are heritable," according to Dr. Roger W. Byard of the Forensic Science Center in Adelaide, Australia.

"Given the recent criticisms of infant death investigations, both in the media and in the literature, there are many reasons why we have an obligation to get it right," Byard writes in an editorial accompanying the study.