The recent heat wave in the Chicago area has now claimed 12 lives.
Autopsy reports released Monday by the Cook County medical examiner's office show heat stress was a secondary factor in the death of a 78-year-old woman. The primary cause of her death was heart disease.
Prior to Monday the death toll was 11. Authorities say most people killed by the heat have pre-existing conditions that are made worse by high temperatures. The last similar heat wave in the region in 1995 resulted in more than 750 deaths over a five-day period.
The Chicago area has since developed a heat response plan that includes more cooling centers and well-being checks to the elderly.
The National Weather Service is predicting highs in the upper 80s for Tuesday.