Heart disease is something like 25% of deaths for white men in the US over 34, according to the CDC. Cancer is another 25% or so - and then the next closest is 10%ish.
Heart disease is a generic term; it covers many things. A lot of it stems from lack of exercise and being overweight. Both of those are affectable by the individual. I have 24kg to lose. :(
Walking is good. I am trying to go on walks with my toddler every evening - when he's in the mood for moving fast, it's a brisk walk.