Three patients with defective heart valves died between January and March 2003 after undergoing operations performed by the same cardiac surgeon at Tokyo Medical University Hospital, informed sources said Saturday.

Another patient also died this January following an operation for heart valve disease that the 45-year-old male surgeon attended as an assistant, they said.

The Tokyo Summary Court ordered the hospital on Friday to preserve evidence, such as the dead patients’ medical charts, at the request of the families of three of the patients, who suspect malpractice, the sources said.

A hospital official said it is now investigating the details surrounding the cases and will make a report to the health ministry, the Tokyo Metropolitan Government and police.

The first three cases involved a 71-year-old woman, who died in January 2003 after having the surgery in October 2002, an 81-year-old woman, who died in January 2003 shortly after undergoing the operation, and a 68-year-old woman, who died in April 2003 following an operation the month before, according to the sources.

The sources said the cardiac surgeon has been involved in a total of 88 heart valve disease operations at the hospital. Of those, he performed 21 operations, they said.