Sotatercept (sotatercept-csrk; WINREVAIR TM ) is an activin signalling inhibitor that is being developed by Merck and Co., Inc. (Rahway, NJ, USA) for the treatment of pulmonary arterial hypertension. Sotatercept recently received approval in the USA for the treatment of adults with pulmonary arterial hypertension [World Health Organisation (WHO) Group 1] to increase exercise capacity, improve WHO functional class and reduce the risk of clinical worsening events. This article summarizes the milestones in the development of sotatercept leading to this first approval for pulmonary arterial hypertension.