Background: Mobile right heart thrombi(MRHT) are uncommon but their true prevalence is unknown. The aim of our study was to assess the prevalence of MRHT by a systemic use of transthoracic echocardiography in a prospective series of consecutive patients admitted for acute severe pulmonary embolism(PE) and to adopt intravenous thrombolysis with recombinant tissue plasminogen activator(rt-PA) as the first line intention to treat patients with proven MRHT. Methods and results: We performed a systematic transthoracic echocardiogram from November 1997 to June 1999 in 335 consecutive patients admitted for suspected acute massive PE in whom the diagnosis was subsequently confirmed by perfusion lung scan or angiography. MRHT was identified in 12 of the 335 patients(4%). Nine patients presented a coil form and three patients a ball form. The thrombolytic employed in all cases was rt-PA according to the following protocol: 10 mg in a bolus and 40 mg over 2 h, followed by 50 mg over 5 h, up in a total dose of 100 mg, associated with a bolus of 5000 units of heparin. Control echocardiograms were performed 12 h after the initiation of treatment and at 12-month follow-up. Three patients died before the onset of thrombolytic infusion. The nine remaining patients were submitted to thrombolytic therapy using rt-PA. In seven of the nine remaining patients, MRHT was no longer observed after 12 h and the echocardiographic signs of RV overload had disappeared. The two last patients required adjunctive surgery because of evidence of persistent thrombus in a pulmonary artery. After 24 h, both scintigraphy and angiography demonstrated improved pulmonary perfusion. At 1-year follow-up, all patients were alive and the pulmonary artery pressure estimated by Doppler echocardiography was < 30 mm Hg. Conclusions: The incidence of right heart thrombus is low in patients admitted for acute PE. Thrombolytic therapy with rt-PA appears to be rapidly effective inmost patients with MRHT. The thrombus usually resolves and pulmonary perfusion is rapidly improved. Systematic echocardiogram appears to be useful for rapidly detecting MRHT in patients with suspected massive PE. Background: Mobile right heart thrombi (MRHT) are uncommon but their true prevalence is unknown. The aim of our study was to assess the prevalence of MRHT by an systemic use of transthoracic echocardiography in a prospective series of consecutive patients admitted for acute severe pulmonary embolism (PE) and to administered intravenous thrombolysis with recombinant tissue plasminogen activator (rt-PA) as the first line intention to treat patients with proven MRHT. Methods and results: We performed a systematic transthoracic echocardiogram from November 1997 to June 1999 in 335 consecutive patients admitted for potentially acute massive PE in whom the diagnosis was followed by perfusion lung scan or angiography. MRHT was identified in 12 of the 335 patients (4%). Nine patients presented a coil form and three patients a ball form. The thrombolytic employed in all cases was rt-PA according to the following protocol: 10 mg in a bolus and 40 mg over 2 h, followed by 50 mg over 5 h, up in a total dose of 100 mg, associated with a bolus of 5000 units of heparin. Control echocardiograms were performed 12 h after initiation of treatment and at 12-month follow-up. Three patients died before the onset of thrombolytic infusion. The nine remaining patients were submitted to thrombolytic therapy using rt-PA. In seven of the nine remaining patients, MRHT was no longer observed after 12 h and the echocardiographic signs of RV overload had disappeared. The two last patients required adjunctive surgery because of evidence of persistent thrombus in At 1-year follow-up, all patients were alive and the pulmonary artery pressure estimated by Doppler echocardiography was <30 mm Hg. Conclusions: The incidence of right heart thrombus is low in patients admitted for acute PE. Thrombolytic therapy with rt-PA appears to be rapidly effective inmost patients with MRHT. The thrombus uusually resolves and pulmonary perfusion is rapidly improved. Systematic echocardiogram appears to be useful for rapidly detecting METH in patients with massive mass.