The man in his 50s was talking to firefighters before he suffered a heart attack while trying to fight the fire himself, according to the sheriff, who spoke to Eyewitness News during an on-air phone interview.
"Fire was on scene, and actually had a conversation with him before he had the heart attack," Villanueva said. "He was transferred to a local hospital but did not survive."
Villanueva offered his condolences to the family of the man, who has not been identified. Additional information on the incident, including the location, was not released.
MORE: Deadly Saddleridge Fire damages homes, prompts evacuations
Villanueva warned residents of the dangers of not evacuating, especially after mandatory orders have been issued.
"If you stay behind in these conditions, you become part of the problem, not the solution," Villanueva said. "Because now we have to effect rescues if people are trapped in homes that are burning down. And then you're clogging the areas that should be clear just for fire and police. Now they're clogged with people that should've left that didn't leave in the right time."
Villanueva stressed the importance of allowing fire crews to battle blazes without aid from civilians.
"When you have 50 to 70 mph wind-blown fire, there's nothing you can do to protect your home," he said. "You can have a fire truck standing right next to your home, and your home is still gonna go down. That's just the sheer force of nature. We have to respect it."
MORE: Time lapse shows fast-moving Saddleridge Fire burning hillside in northern San Fernando Valley
The aggressive brush fire broke out in Sylmar late Thursday night, leaving over 4,700 acres scorched and prompting mandatory evacuation orders for 25,000 homes as flames ripped through residential areas.
At least 45 homes were destroyed in the whipping inferno, with the greatest area of impact on homes lost in Porter Ranch, Los Angeles fire officials said.
MORE: Flames engulf Porter Ranch homes