OBJECTIVE The aim of the present study was to assess the impact of the interval exercise training (IET) vs. steady state exercise training (SSET) on nitric oxide production, through changes of circulating blood markers of endothelial function, including stable end-products of nitric oxide (NOx) and S-nitrosothiols (RSNOs) in patients with left ventricular dysfunction (LVD). METHODS The impact of the IET vs. SSET on NOx and RSNOs production was assessed in a total of 31 (25 male, 6 female) patients with LVD (ejection fraction <40%), who were admitted to our residential rehabilitation centre. Patients were randomised into an IET group (n=18; 15 min interval exercise sessions, 2 times daily) and an SSET group (n=13; 5-10 min steady state exercise sessions, 2 times daily), and exercised every day over a period of 3 weeks. The modified Saville-Griess method was used to determine NOx and RSNOs concentrations. RESULTS A significant increase was observed both for NOx (P < 0.05) and RSNOs (P < 0.001) in the IET group, as well as for RSNOs in the SSET group (P < 0.001). Both training methods were observed to significantly improve exercise capacity, as demonstrated for increased workload (P < 0.001 and P < 0.05 for the IET and SSET groups, respectively) and duration (P < 0.001 and P < 0.01 for the IET and SSET groups, respectively) of the exercise stress test at the end of the study. CONCLUSIONS The results of the present study have demonstrated an increased nitric oxide production and improved exercise capacity in patients with left ventricular dysfunction, who were engaged in an interval exercise programme for three weeks, and clearly indicated an advantage of interval compared to steady state training method for cardiovascular rehabilitation.