Background Carotid duplex ultrasound (CDUS) is often used as a screening test in cardiac patients. Significant cardiac dysfunction may affect the accuracy of CDUS because of alterations in the cardiac cycle. Left ventricular assist devices (LVADs) are frequently implanted as a bridge to cardiac transplant. A review of CDUS in patients with LVADs was performed to assess their influence on arterial waveforms and velocities. Methods Patients with LVADs undergoing carotid duplex in our Intersocietal Commission for the Accreditation of Vascular Laboratories (ICAVL)-accredited vascular laboratory were identified. The carotid waveforms were analyzed qualitatively and quantitatively. Common carotid artery (CCA) and internal carotid artery (ICA) peak-systolic and end-diastolic velocities (PSV and EDV) were recorded as ICA/CCA velocity ratios. In patients with prior CDUS, the changes between these values were analyzed before and after LVAD placement. Results Of the 14 patients with LVADs treated in our institution over the past 2 years, 4 had CDUS (8 ICAs). Mean age was 57 years, and 3 of the 4 patients were men. All patients were free of cerebrovascular symptoms. Qualitatively, there was significant blunting of the CCA and ICA waveforms noted in all 8 ICAs. The degree of stenosis was reported as ≤15% in 7 ICAs and 15–45% in 1 ICA. The mean ICA PSV was 61.8 cm/sec. Two patients (4 ICAs) had CDUS before and after LVAD placement. Comparing pre- and post-LVAD values, the mean ICA PSV decreased by 42% (54 cm/sec; P = 0.04) and EDV increased by 51% (17 cm/sec; P = 0.3). The PSV and EDV ratios were unchanged. Overall assessment of category of stenosis was unchanged in 2 ICAs (≤15%), one decreased from moderate to mild (45–70% to 15–45%), and one ICA changed from 45–70% to ≤15% based on the decreased ICA PSV. Conclusions The presence of an LVAD has a significant influence on CDUS findings. There is a qualitative change in the ICA with blunting of the waveform, and a quantitative change with a decreased PSV and an increased EDV. Compared with pre-LVAD placement, there is a significant decrease in PSV which may affect the accuracy of CDUS using velocity-based criteria. Further study into the accuracy of CDUS in patients with LVADs is necessary.