Hello Your grandmother died , this is very unfortunate . I want to tell you being as physician and doing practice for almost 35 years . Your grandma was a patient of high blood pressure , such type of patient are usually prone to heart disease ( prone to heart attack ) . 2nd reason of heart attack in your grandma case was her age ( as she was 80 years ) . She was taking antihypertensive drugs , old age . Please don t take it otherwise , most of heart attack occurs silently and kills patient at once . Hope you will satisfy . Good luck.