Left-ventricular assist devices (LVAD's) have emerged as the preferred treatment modality for end-stage heart failure, either as a bridge to transplantation or as destination therapy. However, one of the feared complications of LVAD implantation is the development of thrombus within the pump, which is associated with pump malfunction, bleeding, infection, and the need for repeat surgery1. Routine laboratory evaluation and imaging modalities such as echocardiography and CT scanning can help aide in the diagnosis, though uncertainty often remains. Recently, both invasive and non-invasive ramp trials have been described to assess how changes in LVAD speed affect multiple parameters including LVAD flow parameters, left ventricular dimension, and left ventricular filling pressures. This can aide not only in optimizing patient's LVAD function and hemodynamic parameters, but also in the diagnosis of pump thrombosis2,3. A 65-year old male with a history of ischemic cardiomyopathy status post HeartMate II LVAD implantation was admitted to this hospital from clinic after presenting with a one-week history of weakness and chills at home. He had recently undergone pump exchange surgery one month prior to presentation due to an extensive pump thrombosis. Laboratory evaluation on admission showed a mild increase in the patient's baseline LDH and plasma hemoglobin levels. Review of his LVAD log data showed a number of power elevations with associated PI events (Fig. 1). These data raised suspicion for another pump thrombosis and the patient was placed on empiric IV anticoagulation. He then underwent a chest CT-scan with 3-D reconstruction of his LVAD which did not reveal any thrombus (Fig. 2). An echocardiographic ramp study was then performed which showed minimal change in left-ventricular internal diameter when LVAD speed was increased from 9800 rpm to 11,000 rpm (6.9 to 6.4 cm, slope 0.13). Given this mixed picture an invasive hemodynamic ramp study was then pursued which demonstrated unloading of the left ventricle with a significant decrease in LV filling pressures as pump speed was steadily increased (Table 1). This definitively excluded pump thrombosis in this patient and no clear explanation was found for his increased LVAD flows and elevated power readings. He was eventually discharged home from the hospital in stable condition. Pump thrombosis is an extensive cause of morbidity in the LVAD patient population and is one of the primary reasons for pump exchange surgery, as was seen previously in this patient4. This case highlights the difficulty that can be encountered when laboratory and non-invasive imaging studies provide conflicting evidence for the presence of pump thrombosis5. While there have been reports that elevations in power consumption and PI events can occur early on after LVAD implantation and may not be clinically meaningful6, this patient's history of recent pump thrombosis warranted due caution. Ultimately, an invasive hemodynamic ramp study provided much needed clarification on the function of this patient's recently implanted LVAD.