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Atherosclerotic disease has been associated with increased risk of severe neurovascular consequences including transient ischemic attacks, ischemic strokes, and even mortality. Following the onset of carotid stenosis, the brain undergoes different compensatory mechanisms to provide adequate perfusion in order to maintain brain metabolism. In this study, we employed near-infrared spectroscopy (NIRS) to better comprehend how carotid stenosis affects cerebral hemodynamics, both at rest and during activity. Eighteen patients diagnosed with atherosclerotic disease were recruited for a protocol consisting of resting state and vasoreactivity testing performed with breath holding. Although the breath holding challenge induced global vasodilation in all patients, the extent of dilation varied according to the level of stenosis. Patients diagnosed with carotid stenosis have impaired hemodynamic response, with a median 77% vasoreactivity in the hemisphere ipsilateral to the stenotic vessel when compared to the healthy hemisphere. Hemodynamics of these patients differed at rest, with 33% fewer network links in the hemisphere ipsilateral to the stenosis than the healthy hemisphere. On the other hand, hemodynamic patterns were more heterogeneous with patients diagnosed with a carotid occlusion, which correlates with the opening of collateral circulation. Overall, our results suggest that NIRS can open new directions to the investigation of the effects of cerebrovascular atherosclerotic disease.