My Sister Had Always Been Very Health. She Passed Away

My sister had always been very health. She passed away 12/7/2015 in a sudden heart attack. She had chest pain while she was doing 5 miles walk exercise at home. Her HDL was 89. Glucose level was at normal range. I have about the same test result as hers. I like to know what can I do to avoid the same thing happen to me.

Grace