Sheridan testified in San Bernardino Superior Court about the health history and cause of death of each victim - Charles Cunningham, James McDermith, Chad Williams, Robert Taylor and Ralph McWilliams.
They had pre-existing health conditions prior to the fire, but Sheridan believes the fire contributed to the men's deaths.
"The five men would not have died at the time they did," Prosecutor Robert Bulloch said to Sheridan, while he was on the witness stand.
"Yes, it's my opinion that the stress from the fire I believe they would not have died when they did," Sheridan said.
Rickie Lee Fowler, 30, of San Bernardino is accused of lighting the Old Fire in Waterman Canyon, which started on Oct. 25, 2003. He later was indicted by a Grand Jury and faces five counts of murder, arson charges and special circumstances which make him eligible for the death penalty. Prosecutors have said they will seek the death penalty if he is convicted.
The Old Fire scorched more than 91,000 acres, destroyed more than 1,000 structures and cost nearly $38 million.
The five victims, who lived in the burn areas, died from heart attacks that were caused by the stress of evacuation and threats to homes and belongings, Bulloch said.
Cunningham, 93, died at 5:32 p.m. on Oct. 25, 2003. He was classified as obese and had an enlarged heart, Sheridan said.
During defense questioning from attorney Michael Belter, Sheridan said Cunningham did not die directly from smoke inhalation, but from a heart attack.
McDermith, 70, died at 4:24 p.m. on Oct. 25, 2003, of natural causes, specifically heart disease, Sheridan said. McDermith had evidence of past heart attacks and heart surgery. He also had an enlarged heart and was a high-risk candidate for a heart attack, Sheridan said.
Williams, 70, died at 12:25 p.m. Oct. 25, 2003. His cause of death was cardiovascular disease, and he had a history of high blood pressure and chest pain, said Sheridan.
Taylor, 54, died at 11:30 a.m. on Nov. 1, 2003. He had a history of hypertension and had a somewhat enlarged heart, Sheridan said. But his more severe condition was coronary artery disease. Taylor's arteries were severely narrowed and one had 90 percent blockage.
Belter said Taylor was "a heart attack waiting to happen."
Sheridan testified that narrow coronary arteries and an enlarged heart is a bad combination. The stress Taylor was under between when the fire started and when he died was a contributing factor in his death, he said.
McWilliams, 67, died at 5:07 p.m. on Nov. 2, 2003. His cause of death was equal parts lung disease and heart disease, Sheridan said. Before he died, McWilliams was diagnosed with emphysema and bronchitis and was prescribed an oxygen tank.
The defense primarily focused on the men's health problems prior to the fire and it pointed out that the coroner did not find soot or other materials in the victims' lungs at the time of their death.
After Sheridan finished his testimony the prosecution called Fowler's great aunt, Elizabeth Rehkop, to the witness stand.
Rehkop is expected to testify today about recorded conversations she had with Fowler while he was in custody following the Old Fire.