Researchers gathered data from 60 published studies (including over 2 million participants) reporting on the effects of eating nuts on cardiovascular health.

Results: a 1 ounce serving of nuts daily reduced risk of developing or dying from cardiovascular disease by 25%.
1 ounce is about 18-20 walnuts (for example).

The average American eats the equivalent of 2 nuts daily (1/10 of a serving).