Introduction: The role of hyaluronan (HA) was previously demonstrated in patients with idiopathic pulmonary arterial hypertension (PAH). Mitral stenosis (MS) and pulmonary arterial thromboembolism (PTE) are important health problems that can cause pulmonovascular pathology. Pulmonary arterial hypertension develops especially in untreated patients with severe MS and most of patients with PTE. However, there is no data about HA levels in patients with MS and PTE. In this study, we investigated HA levels in patients with rheumatic MS and PTE.