['Animal studies show that nitric oxide is involved in delayed ischaemic preconditioning.', 'To determine whether plasma nitrates/nitrites (NOx-, as measure of nitric oxide) are modified by two consecutive effort tests and whether these changes translate into clinical improvement.', 'There were studied 22 patients with ischemic heart disease, who performed two effort tests at 24-hour interval. Plasma NOx- level was determined and compared before and after both stress tests. Peak effort, double product at peak effort and maximal ST segment depression were considered clinical end-points and were compared between the two tests.', 'Plasma NOx- increased slightly after the first exercise test compared to pre-test value (17.05 +/- 1.6 vs. 15.38 +/- 1.4 micromol/ml). In turn, after the second test a significant rise of NOx- level (23.65 +/- 2.2 vs. 15.10 +/- 1.3 micromol/ml, p < 0.03) was noticed. The pre-test value was practically identical between the two tests. Peak effort and double product at peak effort remained unchanged between the two tests. Although the ischaemic stress was the same, ST depression was significantly lower (p < 0.01) at the second test (0.85 +/- 0.06 vs. 1.73 +/- 0.16 mm).'] Does ischemic preconditioning by repeated exercise tests involve nitric oxide up-regulation?