NORTH HAVEN, Conn. (AP) — A Connecticut firefighter who collapsed while battling a house fire earlier this week died of heart-related problems, according to the state’s chief medical examiner.

Matthias Wirtz, a 22-year veteran of the North Haven Fire Department, had hypertension caused by high blood pressure, hardening of the arteries and an abnormal heart valve, Chief Medical Examiner James Gill said Wednesday.

Fire officials said Wirtz collapsed next to a fire engine outside the four-family home on Monday. First responders at the scene performed life-saving measures on him, but he was later pronounced dead at a hospital. He was 46.

The cause of the house fire, which displaced 13 residents, remains under investigation.

Wirtz started his career as a volunteer firefighter in 1996, serving the North East Volunteer Fire Co. #4 in North Haven. He received numerous letters of commendation over the years and was among the Connecticut firefighters who responded to the terrorist attacks in New York City on Sept. 11, 2001.

A funeral service for Wirtz has been scheduled for Tuesday at St. Elizabeth of Trinity Parish at St. Barnabas Church in North Haven.