This is a big assumption and from what I have researched up to 60% of heart disease is caused by genetics. Environmental pollution and genes play a huge role in both heart attacks and stroke. With dramatic example like:

"In England and Wales, the mortality rate for coronary heart disease (CHD) between 1981 and 2000 have decreased by 62% in men and 45% in women, and more than half of this decline was attributed to a reduction in environmental risk factors."

"This is most strikingly demonstrated by data from China, which show that the age-adjusted CVD mortality rates in Beijing increased by 50% for men and 27% for women because of environmental changes between 1984 and 1999"

I am sure diet and exercise is helpful in preventing heart disease, but it is clear trying to push all responsibility of this disease onto lifestyle choice is highly inaccurate.

You bring up poor being poor as a risk factor. While this may not be true, what is true is poor people's mortality is much higher. See below.

"For example, high-income Asia Pacific and central Latin America have similar age-standardised prevalence of ischemic heart disease (about 2600 cases per 100,000), but the mortality rate due to ischemic heart disease in central Latin America is four times that in high-income Asia Pacific (109 vs 26 per 100,000, respectively). "

So same prevalence, but a huge difference in mortality.