Police and firefighters in Delaware County responded to a Bethel Township home at about 2:40 p.m. Thursday, where they found the fire already extinguished.
The medical examiner's office says 83-year-old Shirley McGinniss of Garnet Valley was an "inadvertent victim of clothing ignited within kitchen."
Medical Examiner Fredric Hellman said McGinniss died of "soot and smoke inhalation and extensive thermal burns." He ruled her death accidental.
He said Saturday that coronary artery disease complicated by rheumatic heart disease contributed to her death.