Thrombus formation inside of the pump is a major cause for device malfunction following the left ventricular assist device (LVAD) implantation. We recently established a novel ramp test protocol facilitating continuous bedside echo monitoring to optimize LVAD function and diagnosing device malfunctions. We describe a case of 29-year-old woman undergoing HeartMate II LVAD implantation, in whom serial ramp studies were used to diagnose intra-device thrombus after device implantation. The 1st ramp study at postoperative day (POD) 26 revealed adequate reduction in ventricular size according to the increase in LVAD speed (left ventricular end-diastolic diameter [LVEDD] at minimum and maximum speeds, 68 and 37 mm, respectively). The patient was discharged home and received routine anticoagulation maintenance therapy. However, a 2nd ramp test was performed on POD 56 due to increased lactase dehydrogenase and brain natriuretic peptide levels and showed marked increase in left ventricle (LV) chamber size without adequate response to the LVAD speed changes (LVEDD at minimum and maximum speeds, 88 and 76 mm, respectively). Given the suspicion for partial pump thrombosis, the patient was immediately hospitalized and received intravenous heparin infusion. After the optimization of the intensive anticoagulation therapy, the patient underwent a 3rd ramp study, which showed a remarkable improvement of the adequate response to LVAD speed changes. The patients eventually underwent cardiac transplant successfully, and the partial clot was found inside of the pump. This case demonstrates the usefulness of serial ramp studies in patients who are suspected to have device thrombosis.