Acute pulmonary embolism (PE) is a major cause of morbidity and mortality in hospitalised patients. While the vast majority of patients with PE survive, a subset die, mostly within a few hours of presentation. Anatomically massive pulmonary emboli account for only half these deaths, while submassive or recurrent embolism accounts for the other half. There are increasing reports of patients with PE, normal blood pressure and no shock who have significant right heart dysfunction. In large registry-based cohorts, patients with right ventricular dysfunction have worse clinical outcomes. Rapid anticoagulation of the haemodynamically stable patient with PE is associated with excellent outcomes. There is also evidence to support the use of thrombolysis in patients with massive PE. However, the optimal management of patients with submassive PE is controversial. This article looks at the definition and diagnosis of submassive PE, and systematically reviews the role of thrombolytic therapy in this subgroup of patients.