Hi, My Grandfather Had A Heart Attack At Night Around

Hi, my grandfather had a heart attack at night around 1 am. we thought its just gastric problem and gave him some medicines and he was fine. In the morning we took him to the hospital and after seeing his ECG, doctor said he had a heart attack already and 48 hours are critical and we just can observe. And at around 3 30 pm, he had a severe attack again and he died unfortunately. Were the doctors right? He couldn't be treated? He was at the age of 80.