Acute pulmonary embolism (PE) is a common disease which frequently results in life-threatening right ventricular (RV) failure. High-risk PE, presenting with hypotension, shock, RV dysfunction or right heart thrombus is associated with a high mortality, particularly during the first few hours. Accordingly, it is important to commence effective therapy as soon as possible. In the case described in this report, a 49-year-old woman with myotonic dystrophy type 1 presented with acute respiratory failure and hypotension. Transthoracic echocardiography showed signs of right heart failure and a mobile right heart mass highly suspicious of a thrombus. Based on echocardiographic findings, acute thrombolysis was performed resulting in hemodynamic stabilization of the patient and complete resolution of the right heart thrombus. This case underscores the important role of transthoracic echocardiography for the diagnosis, management and monitoring of PE and underlines the efficacy and safety of thrombolysis in the treatment of PE associated with right heart thrombus.