Abstract: Gap junctions are proteins made of connexins which are involved in the regulation of vascular function. Deletion of connexins 43 (Cx43) modifies expression of genes known to be involved in the regulation of the vasculature, differentiation and function of vascular cells. Interestingly, mutant mice lacking endothelial nitric oxide synthase (eNOS) gene have been shown to be hypertensive, suggesting that nitric oxide (NO) plays a role in the physiological control of blood pressure. It was therefore hypothesised that the endothelial deletion of Cx43 in the pulmonary vasculature induces endothelial dysfunction and causes eNOS impairment thereby reducing NO biosynthesis, thus leading to vasoconstriction and vascular remodelling which subsequently leads to the development of pulmonary arterial hypertension (PAH).