Patients with a left atrial (LA) thrombus are considered at high risk of thromboembolic events. Reports about thrombolytic therapy are limited and optimal guidelines are lacking. In this report, a large, pedunculated, highly mobile thrombus of the LA attached via a short stalk to the LA appendage brim in a 59-year-old female with atrial fibrillation is described. The patient was treated with 100 mg intravenous tissue plasminogen activator for 2 h after the ineffective administration of herapin. The thrombus soon dissolved. However, the patient developed a transient ischemic embolism 12 h later when the post hoc heparin effect was at its nadir. Based on this and other reports, thrombolytic therapy may be effective and safe in patients with acute, non-organized LA thrombi and post hoc heparinization should be sufficient to prevent thromboembolism from rebound coagulation.