Clonal hematopoiesis, a condition in which individual hematopoietic stem cell clones generate a disproportionate fraction of blood leukocytes, correlates with higher risk for cardiovascular disease. The mechanisms behind this association are incompletely understood. Here, we show that hematopoietic stem cell division rates are increased in mice and humans with atherosclerosis. Mathematical analysis demonstrates that increased stem cell proliferation expedites somatic evolution and expansion of clones with driver mutations. The experimentally determined division rate elevation in atherosclerosis patients is sufficient to produce a 3.5-fold increased risk of clonal hematopoiesis by age 70. We confirm the accuracy of our theoretical framework in mouse models of atherosclerosis and sleep fragmentation by showing that expansion of competitively transplanted Tet2−/− cells is accelerated under conditions of chronically elevated hematopoietic activity. Hence, increased hematopoietic stem cell proliferation is an important factor contributing to the association between cardiovascular disease and clonal hematopoiesis. Display omitted •HSC proliferation is elevated in mice and humans with atherosclerosis•Increased proliferation accelerates somatic evolution and clonal hematopoiesis (CH)•Measured rates imply several-fold increased risk of CH in atherosclerosis patients•Mutant expansion is accelerated in mice with increased HSC proliferation Heyde et al. propose that clonal hematopoiesis can be a symptom rather than a cause of atherosclerosis, since this disease increases hematopoietic stem cell division, which results in accelerated somatic evolution.