Fewer people in the U.S. are succumbing to preventable death from cardiovascular disease, but most of the improvement in rates is among the elderly, rather than among younger adults who are also at risk, according to federal data released Tuesday.

The rate of so-called avoidable deaths from heart disease, stroke and hypertension declined 29% between 2001 and 2010 in people under age 75, thanks in part to healthier lifestyles and better cardiac care, according to an analysis of U.S. mortality data by the Centers for Disease...