This study was designed to test the hypothesis, developed from our previously completed work, that a high level of dietary K + intake would reduce the severity of restenosis lesion development in the swine coronary artery following balloon angioplasty. Two groups of 7 castrated male swine were studied; for 28 days the normal K + group (NK) consumed a diet containing 0.25% K + and the high K + group (HK) ate diet containing 2.0% K + . After 14 days on the diet, balloon angioplasty was performed, dilating the proximal portion of the left circumflex artery (LCX) to 25 to 30% greater than the resting diameter. After an additional 14 days on the same diets the animals were sacrificed, the hearts removed and normal and lesioned sections of the LCX was analyzed histologically. Morphometric measurements were carried out for analysis of the neointimal thickness (NT), neointimal area (NA), ratio of neointimal area to total wall area (N/W), and thrombus score (TS; range 0 to 5). At the time of angioplasty, plasma K + in the NK group averaged 3.07 +/- 0.19 mM, and the HK plasma K + was 3.95 +/- 0.12 mM (p < 0.01), while plasma renin activity averaged 1.01 +/- 0.22 and 0.41 +/- 0.16 ngAl/ml/hr in the normal and high K + groups, respectively. The morphometric data are presented below: High dietary K + intake strongly inhibits restenosis lesion development following balloon angioplasty in the swine coronary artery. High K + intake may be beneficial for patients undergoing balloon angioplasty.