Real-time noninvasive cerebral blood flow monitoring during cardiac surgery could decrease rates of neurologic injury associated with hypothermic circulatory arrests (HCA). We used combined frequency domain near-infrared spectroscopy and diffuse correlation spectroscopy (FDNIRS-DCS) to measure cerebral oxygen saturation and an index of blood flow (CBFi) in 12 adults undergoing HCA. Our measurements revealed negligible CBFi during retrograde cerebral perfusion (RCP: CBFi 91.2%±3.3% drop; HCA-only: 95.5%±1.8% drop). There was a significant difference during antegrade cerebral perfusion (p = 0.003). We conclude that FDNIRS-DCS can be a powerful tool to optimize cerebral perfusion and that RCP’s efficacy needs to be further examined.