Updated 3 hours ago NBC Universal, Inc. After a study found the majority of people who had a heart attack were unaware of it, a Walpole woman is sharing her own experience as a warning to others. Researchers at Harvard Medical School looked at about 2,000 people who showed evidence of a heart attack and found that 80% were unaware that they had one. Walpole resident Patti Chu said this can be dangerous and even life-threatening. Download our mobile app for iOS to get alerts for local breaking news and weather. “I cannot pinpoint any specific day that I thought I was having a heart attack," Chu said.