Introduction <p>Tumours have heterogenous and dysfunctional vasculature that can cause a therapeutic barrier for intravenous chemotherapy delivery. As tumours do not vasoconstrict, aerobic exercise may acutely increase tumour blood flow through increased cardiac output and potentially increase chemotherapy delivery. While pre-clinical studies have demonstrated increased tumour blood flow with moderate intensity aerobic exercise, no clinical studies have assessed this effect. This study examined the effect of acute aerobic exercise at varying intensities on tumour blood flow in people with liver metastases.</p> Methods <p>Participants with stage IV cancer with liver metastases performed an exercise test followed by three 5-minute bouts of light, moderate and high intensity cycling. Doppler ultrasound assessed blood flow to the hepatic artery (control) and liver tumour at baseline and after each exercise bout for 10&#xa0;min.</p> Result <p>Eight participants completed the study, however, three were excluded from analysis due to a lack of sonographer confidence to identify and measure tumour vessels, due to small size and poor accessibility. There was 152% increase in blood flow (peak systolic velocity) to the tumour after moderate intensity exercise (24.63 ± 5.66 to 37.56 ± 5.91, <i>p</i> = 0.043), and an increase in tumour and hepatic arterial resistance (resistive index) after high intensity exercise (0.65 ± 0.14 to 0.74 ± 0.15 and 0.81 ± 0.15 respectively, <i>p</i> = 0.043).</p> Conclusion <p>Moderate intensity exercise acutely increases blood flow to metastatic liver tumours. These findings support future work to examine whether aerobic exercise improves clinical outcomes such as chemotherapy delivery and efficacy, particularly when delivered concurrent to infusion.</p>