One of the complications that can occur with continuous, axial-flow left ventricular assist devices (LVADs) is thrombosis within the left ventricle, adjacent to the device's inflow conduit, which may cause inflow obstruction and recurrent heart failure. We describe 2 cases in which we used a catheter to continuously infuse recombinant tissue plasminogen activator (tPA) into the left ventricle until signs of successful thrombolysis was achieved. By monitoring the result and administering only as much tPA as necessary to achieve thrombolysis, we were able to successfully lyse the obstructing thrombus with a minimal dose of tPA without causing any significant bleeding problems. This technique may be useful for managing this potentially serious complication while minimizing the risk of treatment.