What Could Be The Probable Cause Of Death?

Hi Doctor,

My dad passed away on 12 Sept 2011 night at age 73. He has high blood pressure(controlled). Last year itself, he feel dizzy and my sister brought him to see doctor, and after doctor consult him, he just suggest him to reduce the high blood pressure tablet from 1 to 1/2 tablet. Everymonth my sister did bring my dad to do urine test and it seems fine, and i am not sure whether he has any chest pain all the while as he never mention to us. On that day, we are not around with him, according to the people, they said my dad sat on the chair and drink water....then they said my dad is like feel dizzy and unconcious but still have heart beat. firstly they said the heart beat is very fast and slowly slow down , he graps his hand tight and he just die within 20 minutes, i feel sad becuase i was not around with him. And when doctor arrive he said the heart beat is stop and pronouce my dad has gone. I just wanted to know what is the causes for his death since we do not perform any post mortem on him. Can he be saved if got CPR? Is it my mistake that i never suggest him for a blood test?

Thanks You,
Vivian