Objective: Cardiac resynchronisation therapy (CRT) has emerged as a new treatment strategy for a subgroup of patients with heart failure. In this study, we aimed to evaluate acute effects of CRT on cerebral blood flow. Material and methods: Twenty-two (six female and 16 male) patients (mean age 60.8 ± 5.3 years) with idiopathic dilated cardiomyopathy were enrolled in the study. Blood flow in the common carotid artery (CCA), internal carotid artery (ICA), and vertebral arteries (VA) was evaluated by Colour Doppler ultrasound. All measurements were performed at a constant heart rate of 90. beats/min for excluding the influence of variant heart rates. Results: Flow velocities, flow volume, resistivity and pulsatility indices which were correlated with cardiac output (CO) significantly increased after CRT. The only parameter affecting the change in mean velocity and flow volume in VA was the change in the CO (β= 1.1, p=0.02 and β=1.2, p=0.04, respectively). The change in peak systolic velocity after CRT in VA and the change in mean velocity and volume in ICA were affected by the change in the CO (β= 1.2, p= 0.007; β= 0.8, p= 0.08 and β=0.6, p=0.03, respectively). The change in total cerebral blood flow was also affected by the change in CO (β= 1.3, p= 0.003). Conclusion: CRT increases the carotid and vertebral artery blood flow velocities, flow volumes and therefore improves cerebral blood flow. This improvement in the cerebral blood flow after CRT is largely due to the increase in the cardiac output. © 2012 Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ).