OBJECTIVE: The aim of this study was to investigate the effects of high intensity interval training (HIIT) versus moderate intensity continuous training (MICT) in heart failure patients with reduced ejection fraction (HFrEF). BACKGROUND: Despite the well-known positive effects of exercise in heart failure patients, the best mode of exercise is still under discussion. METHODS: We searched Pubmed/MEDLINE, Cochrane Central Register of Controlled Trials, PEDro data base, and SciELO (from the earliest date available to October 2017) for randomized controlled trials that evaluated the effects of HIIT versus MICT in HFrEF patients. Weighted mean differences (WMD) with 95% confidence interval (CI) were calculated, and heterogeneity was assessed using the I(2) test. RESULTS: 13 studies met the study criteria, including 411 patients. Compared to MICT, HIIT resulted in improvement in Peak VO(2) WMD (1.35 mL·kg(-1)·min(-1) 95% CI: 0.03 to 2.64 N = 411). HIIT resulted in no difference in VE/VCO(2) slope WMD (-1.21 95% CI: -3.0 to 0.58 N = 135), and quality of life measured by Minnesota Living with Heart Failure questionnaire WMD (1.19 95% CI: -5.81 to 8.19 N = 79). Sub-group analyses comparing studies with and without isocaloric exercise training protocol also showed a nonsignificant difference in peak VO(2) for participants in the HIIT group compared with MICT group. CONCLUSIONS: HIIT improves peak VO(2) and should be considered as a component of care of HFrEF patients. However, its superiority versus MICT disappears when isocaloric protocols are compared. An important caveat is uncertainty and variation of actual training intensities compared to program targets.