110 patients will be randomized in the study. The patients included in the study will be randomized, in a double blind fashion, to receive rt-PA 100mg 2h (55 patients) or rt-PA50mg 2h(55 patients).Study treatment should be administered within 72 hours from echocardiography. Echocardiography will be repeated at 24 hours and 14 days from rt-PA injection. A Follow-up visit at 14 days from randomization will include: clinical history, physical examination and ECG and an echocardiographic examination CTPA and V/Q scan.