INTRODUCTION Pulmonary arterial hypertension (PAH) is still an incurable disease with high mortality despite recent treatment advances. Chronic thromboembolic pulmonary hypertension (CTEPH) is a specific form of pulmonary hypertension due to thromboembolic occlusion of pulmonary arteries. Although 50 - 60% of the CTEPH patients can be cured via pulmonary endarterectomy (PEA), a significant portion is inoperable. For both diseases, therefore, new treatments are urgently needed. AREAS COVERED The review will explain the mechanism of action of the soluble guanylate cyclase stimulator riociguat (BAY 63-2521) and will give an overview regarding the current scientific and clinical data of riociguat in both indications PAH and CTEPH. The most relevant publications up to date were used as sources for this review. EXPERT OPINION Riociguat is a novel treatment option in PAH class 1, which, in contrast to phosphodiesterase-5 inhibitors, acts independently of endogenous nitric oxide and has shown efficacy in combination therapy with endothelin-1 receptor antagonists. Riociguat is the first approved drug for non-operable CTEPH and sustained CTEPH after PEA, thus introducing a proven pharmacologic treatment option for this group of patients. Long-term results in the real-life setting are still lacking and are needed to provide evidence for the true amount of progress riociguat adds to the field.