Acute rises in pulmonary artery pressures are associated with a significant mortality and morbidity due to the significant strain on the right ventricle. Although hydrogen sulphide (H2S) has been studied for its potential role in the systemic circulation, little is known of its effects on the pulmonary circulation in humans. We studied the effect of H2S at both the human isolated pulmonary arterial level as well as the human isolated perfused lung level.