To investigate the time course of restenosis, serial treadmill exercise testing was performed in the absence of medical therapy by 31 patients with single vessel coronary disease who underwent successful angioplasty. Exercise tests were performed before angioplasty and at 3 days and 1, 3 and 6 months after angioplasty; if the test was positive, it was repeated after administration of 10 mg of intravenous verapamil. At arteriography 6 months after coronary angioplasty, 17 patients (group 1) showed no restenosis but 14 patients (group 2) did. Before angioplasty all 31 patients had a positive exercise test with ST segment depression greater than or equal to 1 mm. At 3 days after angioplasty, three patients in group 1 had a positive exercise test compared with 11 patients in group 2 (p = 0.08). At 1, 3 and 6 months, 1 patient in group 1 had a positive exercise test compared with 14 patients in group 2 (p less than 0.01). The heart rate-blood pressure product (beats/min.mm Hg) calculated at 1 mm ST segment depression, or at peak exercise if the test was negative, was used as an index of the ischemic threshold. In group 1 (no restenosis) the ischemic threshold increased progressively from 14,840 +/- 1,075 (mean value +/- SEM) before angioplasty to 21,210 +/- 1,049 at 3 days and to 25,140 +/- 1,177 (p less than 0.001) at 6 months. In group 2 (restenosis) the ischemic threshold increased from 16,270 +/- 828 before angioplasty to 20,400 +/- 984 (p less than 0.0004) at 3 days but decreased to 16,090 +/- 1,298 (p less than 0.006) at 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)