Heart attacks continued to be the leading cause of fatal on-duty injury to U.S. firefighters - 40 deaths, or 39 percent of all firefighter deaths in 2000, according to a report released from National Fire Protection Association.

There were 102 on-duty firefighter deaths, a decrease of 10 deaths from 1999.

On-duty heart attack deaths are usually attributed to overexertion or stress. The stress-related deaths in 2000 also included two due to strokes, one to an aneurysm and one from a seizure. Last year, 11 of the 40 who suffered fatal heart attacks were known to have had prior heart problems, including heart attacks or bypass surgery.

Last year, 21 firefighters were killed in motor vehicle crashes, almost half of which occurred while the victims were responding to emergency calls. Thirteen firefighters died of smoke inhalation or burns at fires, 12 died of traumatic injuries resulting from falls or from being struck by vehicles or other objects, and three firefighters were murdered while on duty.