Left ventricular assist device (LVAD) implantation is an established treatment for patients with advanced heart failure. To date, studies evaluating the impact of aerobic training in patients with LVADs have focused on moderate-intensity exercise.This pilot randomized controlled trial compared the effects of high-intensity interval training (HIIT) with those of moderate-intensity continuous training (MICT) on peak oxygen consumption (V̇O peak) in patients with LVADs. Secondary outcomes included 6-minute walk test distance, flow-mediated dilation, and anthropometry. Assessments were conducted at baseline and after 12 weeks of supervised training performed 3 times weekly. Participants were randomized to HIIT (4 sets of 4 minutes at 80%-90% V̇O reserve, alternating with 3 minutes at 50%-60% V̇O reserve) or MICT groups (28 minutes continuously at 50%-60% V̇O reserve). Within and between-group differences were analyzed using linear mixed models. Data are expressed as marginal means with 95% confidence intervals or as mean ± SD.2A total of 21 participants were randomized (HIIT: age 57.7 ± 13.1 years; n = 11 and MICT: age 55.6 ± 14.2 years; n = 10) (mean ± SD). No major adverse events occurred in response to training in either group. HIIT significantly improved V̇O peak (15.6 [13.2-17.8] to 18.4 [16.0-20.8] ml/kg/min) (marginal mean [95% CI]) compared with MICT (16.2 [13.8-18.7] to 17.2 [14.6-19.7] ml/kg/min; p < 0.05 between groups). No significant group differences were detected in secondary outcomes.2In patients with LVADs, HIIT was well tolerated and increased aerobic capacity more than MICT. These preliminary findings support the prescription of high-intensity exercise in clinically stable patients with LVADs but warrant validation in a larger sample and across a broader range of physiologic and clinical outcomes.URL: https://www.anzctr.org.au, unique identifier: ACTRN12616001596493.