Background. It has been proposed that high-heeled shoes may contribute to the development and progression of knee pain. However, surprisingly little research has been carried out on how shoe heel height affects muscle activity around the knee joint. The purpose of this study was to investigate the effect of differing heel height on the electromyographic (EMG) activity in vastus medialis (VM) and vastus lateralis (VL) during a sit to stand activity. This was an exploratory study to inform future research. Methods. A repeated measures design was used. Twenty five healthy females carried out a standardised sit to stand activity under 4 conditions; barefoot, and with heel wedges of 1, 3, and 5 cm in height. EMG activity was recorded from VM and VL during the activity. Data were analysed using 1 × 4 repeated measures ANOVA. Results. Average rectified EMG activity differed with heel height in both VM (F 2.2, 51.7 = 5.24, p < 0.01), and VL (F3, 72 = 5.32, p < 0.01). However the VM: VL EMG ratio was not significantly different between conditions (F3, 72 = 0.61, p = 0.609). Conclusion. We found that as heel height increased, there was an increase in EMG activity in both VM and VL, but no change in the relative EMG intensity of VM and VL as measured by the VM: VL ratio. This showed that no VM: VL imbalance was elicited. This study provides information that will inform future research on how heel height affects muscle activity around the knee joint.