It's possible to walk down the expressway blindfolded and not get hit. In fact, if you took 1000 people and had them walk a mile or so, there would probably be more than one who survived.
But that wouldn't mean that it was safe, or smart.
So, while genetics are definitely a big part - truth is you can't do anything about them. We do KNOW that certain things are directly correlated with blocked arteries, and we know a lot about them.
If you smoke, your yearly risk of heart attack is twice what it would be otherwise
The higher you cholesterol and blood pressure, the higher your risk of heart attack.
and so on.
There are enormous piles of data showing direct connection between risk factors and bad outcomes. But like anything else, there are no guarantees either way.
In the end the question is: Which risk group do you want to be in? The one with better odds, or the one with worse odds? You can't control life, but your choices definitely influence what happens. And like Daddog implied, if the odds play out the wrong way your life can be much, much less pleasant than you wish.