Dasatinib, a second-generation tyrosine kinase inhibitor used for treating chronic myeloid leukaemia (CML), is associated with rare but significant adverse effects, including pulmonary arterial hypertension. This condition is thought to result from endothelial dysfunction and vascular remodelling linked to Src kinase inhibition. Symptoms such as progressive dyspnoea and fatigue may appear months or years after starting therapy, emphasising the need for long-term vigilance. We present the case of a 55-year-old female with CML who developed severe pre-capillary pulmonary hypertension after prolonged dasatinib use. Diagnosis was confirmed via echocardiography and right heart catheterisation, with other causes excluded. Following dasatinib discontinuation, initiation of targeted PAH therapy, and replacement with imatinib, the patient showed significant clinical and haemodynamic improvement.