There is marked sexual dimorphism displayed in the onset and progression of pulmonary hypertension (PH). Females more commonly develop pulmonary arterial hypertension (PAH), however, females with PAH and other types of PH have better survival than males. Pulmonary microvascular endothelial cells play a crucial role in the pulmonary vascular remodelling and increased pulmonary vascular resistance of PH. Given this background, we hypothesized that there are sex differences in the pulmonary microvascular endothelium basally and in response to hypoxia that are independent of the sex hormone environment.