Dyspnoea is a principal presenting symptom in pulmonary arterial hypertension (PAH), and often the most distressing. The pathophysiology of PAH is relatively well understood, with the primary abnormality of pulmonary vascular disease resulting in a combination of impaired cardiac output on exercise and abnormal gas exchange, both contributing to increased ventilatory drive. However, increased ventilatory drive is not the sole explanation for the complex neurophysiological and neuropsychological symptom of dyspnoea, with other significant contributions from skeletal muscle reflexes, respiratory muscle function, and psychological and emotional status. In this review, we explore the physiological aspects of dyspnoea in PAH, both in terms of the central cardiopulmonary abnormalities of PAH and the wider, systemic impact of PAH, and how these interact with common comorbidities. Finally, we discuss its relationship with disease severity.