Background: Previously, we reported that elevated extracellular potassium concentration in vitro inhibited proliferation and migration of vascular smooth muscle cells, formation of free radical compounds by macrophages, and reduced platelet sensitivity to agonists. More recently, we described a reduction in neointimal proliferation after balloon angioplasty injury in the carotid arteries of rats associated with an elevation of dietary potassium intake during a 4-week experiment. In the present study we conducted a similar investigation in the swine coronary artery balloon angioplasty model. Procedures: Two groups of seven castrated male swine were studied; for 28 days the normal potassium group consumed a diet containing 0.25% potassium and the high potassium group ate diet containing 2.0% potassium. After 14 days on the diet, balloon angioplasty was performed. After an additional 14 days on the same diets the hearts were removed, and normal and lesioned sections of the artery were analyzed histologically. Results: The neointimal area was markedly less in the high potassium group than in the normal potassium group, 0.33 ± 0.04 mm2 v 0.7 ± 0.10 mm2(P< .004). Neointimal area-to-total wall area ratio in the normal potassium group averaged 0.199 ± 0.018, significantly greater than the ratio computed for the elevated potassium group, 0.120 ± 0.015 (P < .006). Conclusion: These results support the hypothesis that a high level of dietary potassium intake inhibits neointimal proliferation after balloon angioplasty in the swine coronary artery. © 2001 American Journal of Hypertension, Ltd.