(WSBT) They're often labeled as some of the bravest, the strongest and the most heroic. But the most dangerous and potentially deadly thing firefighters face isn't always a fire. That silent killer is heart disease, and it's also the number one cause of death for firefighters.

North Liberty Fire Chief Gene Patrick knows the danger first hand. He knew his passion for fighting fires was dangerous, but he never thought his toughest battle would be his health.

“I was an avid walker, jogger…I did everything,” he said.

But 3 and a half years ago, Patrick had a heart attack — and collapsed at a barn fire.

“I guess one of the firemen from Walkerton walked up to me and asked if I was OK and I said 'no' and that's the last I remember,” Patrick told WSBT News. “Just fell over backwards and that was it. I was out.”

That's the day he became a statistic. A recent study shows nearly half of all firefighter deaths are caused by heart disease; and their risk of cardiac death is 10 to 100 times higher while they're fighting fires.

"One of the biggest things is you go from zero to wide open in just a matter of minutes, and it's really hard on your body,” said Chief Patrick. “You wake up from a dead sleep and take off runnin' … no warm up time."

More than 10 area fire departments require annual physicals. Certified Physician’s Assistant Carrie Barbus oversees those medical exams.

“Every firefighter knows somebody who went down,” she said. “They don’t want it to be them and they don’t want it to be anyone they know.”

Barbus said she often has to get tough with the firefighters.

"We wave a standard in front of a guy's face and say 'Listen...do you wanna be the one that goes down on the call and puts your brothers and sisters at risk? The people you're trying to save at risk?’"

Several local fire departments are taking a pro-active approach to fighting heart disease. The Clay Township Fire Department has a certified fitness trainer working every shift.

“We have about 80 percent of our firefighters who participate in a fitness program," said Dan Baughman, the department’s trainer.

They've also developed better eating habits with the help of a nutritionist. But these changes aren’t easy for everyone to make.

Physician’s Assistant Carrie Barbus says her biggest concerns are things like out of control hypertension, family history, smoking and smokeless tobacco."

Dan Baughman says there are individuals on the department that he likes to target more than others when it comes to fitness.

“Those 20 percent that don't participate are the ones that I target a little more."

North Liberty's Gene Patrick has some advice for firefighters who aren't getting the message.

“They need to start physical fitness early and stay with it, and it makes it easier for them."

More than 70 percent of fire departments in the country are volunteer departments — just like Chief Patrick's in North Liberty. Those smaller departments have a much smaller call volume than paid departments. That means they also get less money for things like fitness equipment and health programs.