Background: Heart and brain interaction is a well-known entity in heart failure (HF) and left ventricular systolic dysfunction poses an increased risk for stroke and cognitive impairment. Transcranial Doppler (TCD) provides valuable information on cerebral blood flow velocities (CBFV). However, less is known about CBFV in HF patients with reduced EF. So, we aimed to evaluate CBFV by means of TCD in patients with HF and reduced ejection fraction (HFrEF). Methods: This study included 46 HFrEF patients (mean age 65.2?11 years, mean EF 20.1?3.8%) who underwent to TCD examination. In addition, 26 healthy individuals with sinus rhythm and EF >50% were included in the study as a control group. Peak systolic, mean and end diastolic flow velocities of the both right and left middle cerebral artery (RMCA and LMCA) were analyzed. In subgroup analysis, HFrEF patients compared according to rhythm. Correlation analyses was performed in HFrEF group between EF and TCD velocities. Results: The average of RMCA and LMCA peak systolic and mean flow velocities were significantly lower in HF patients than those in control group (76,06?23,7 cm/s and 48,49?16,4 cm/s in HF group vs 87,84?14,5 cm/s and 56,41?10,7 cm/s in control group, p=0,025 and p=0,016, respectively, for RMCA and 75,1?22,3 cm/s and 47,57?14.8 cm/s in HF group vs 88,73?17,7 cm/s and 57,15?12,4 cm/s in control group, p=0,009 and p=0,007, respectively, for LMCA). The average mean flow velocity of RMCA and LMCA was significantly lower in HFrEF patients with AF than HFrEF patients with sinus rhythm. (P=0.04 and P= 0.03, respectively) In correlation analysis, EF was significantly positively correlated with both LMCA and RMCA flow velocities in HFrEF group. Conclusion: This study showed that HFrEF patients have lower CBFV as compared to healthy controls and HFrEF patients with AF rhythm have lower CBFV compared to HFrEF with sinus rhythm which might be one of the explanations of the adverse interaction between heart and brain in HFrEF.