welcome to HCM,
i want to tell you that heart attack
and heart failure
are the two different things.
as your father had third heart attack and his heart function is 20%. so he may be in heart failure..
heart attack is due to acute blockage of supply of the heart.
and heart failure is pump failure that is heart is unable to give supply to all the body parts.
in my opinion you should not go for any aggressive approach becoz he is already 69 and paralytic and had 3 attack.
you can go for treatment for heart failure by a cardiologist.
wish that ur father get a good health..