I can tell you exactly why people had less heart attacks in the old days because I can still remember. Of course, they worked harder then but, most importantly, they:
1. ate raw, unpasturized dairy products made from grass fed cows and free-run chicken eggs
2. ate range fed animals (not grain or otherwise fed)
3. Baked their own breads, desserts
4. Were not afraid of eating saturated fat such as butter or lard
5. did not eat soy products, powdered proteins, anything processed.

In other words, they ate pure, unrefined, unprocessed, natural foods. No they did not eat low-carb per se but they also did not eat all the garbage, low-carb or no, that we eat today that contain chemicals, poisons and fillers and almost no nutrition.