The pediatric population is highly impacted by brain tumours, as they are the most common type of solid tumour affecting children. Medical advances have improved the survival rate of children with brain tumours, but many survivors still experience late effects. In adulthood, 18% of pediatric brain tumour (PBT) survivors have reported cardiovascular issues such as strokes, blood clots, and angina, but little is known about the cardiovascular health of these survivors during childhood. The primary objective of this thesis was to measure the proportion of PBT survivors with values of body mass index (BMI), waist circumference (WC), and aerobic fitness meeting the cut-offs associated with unfavourable cardiovascular health (BMI≥+2 SDs, WC≥90th percentile, and % peak oxygen uptake (VO2peak) predicted<85%). The secondary objective was to observe the effects of 12 weeks of exercise training on the BMI, WC, blood pressure (BP), and aerobic fitness of PBT survivors and describe the feasibility of an exercise training program for this population. In this thesis, 32 PBT survivors who had all received cranial radiation were included (age=12.3±3.4 years, age at diagnosis=7.0±2.5 years, time since treatment completion=4.5±2.8 years, 21/32 male). While WC was measured for 13/32 participants, BMI and aerobic fitness were measured for all. Of the participants, 5/32 children completed a 12-week pilot exercise program consisting of two group and two in-home exercise sessions per week. A control group (n=2, age=14.8±3.6 years, 1/2 male) and an intervention group (n=5, age=15.0±2.3, 3/5 male) had BMI, WC, BP, and aerobic fitness measurements taken pre- and post-training. Of the participants, 15.6% (5/32) had a BMI≥+2 SDs, 30.7% had a WC≥90th percentile, and 86.7% had a %VO2peak predicted<85%. In total, 81% (26/32) of the participants had at least one identified biomarker reflecting unfavourable cardiovascular health. A training effect was only observed in BP (change of +9%). The exercise program was feasible with an adherence rate of 88% (21/24) to the group and in-home sessions. All (5/5) participants completed the program without injuries or adverse events during the training program. Findings from this thesis indicate that 81% brain tumour survivors have at least one biomarker indicating unfavourable cardiovascular health in childhood. This thesis also provides novel information to be considered before implementing exercise as a therapy for improving the cardiovascular health of survivors. Future additional research is required to determine the appropriate duration, frequency, and intensity of aerobic exercise to stimulate a training effect on these cardiovascular biomarkers. / Thesis / Master of Science (MSc)