How can i stop worrying? driving me mad?

my dad had a heart attack a few years ago and still smokes (not as much but still a bit) and there is no way he will quit. i just dont want him to die within the next few years. can a healthy diet and excersize 'balance' out the smoking? he smokes lowest tar and nicotine and only about 6-8 a day. he is also still on tablets. please dont say 'cherish the moments you have' because that makes me even more upset. how can i stop worryng all the time!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!