Signal detection in the analysis of blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) may be greatly hindered by cardiac pulsatility artifacts. Vessel pulsation, cerebrospinal fluid movement, and tissue deformation are all associated with the cardiac cycle and all can produce fMRI signal variance. Most cognitive fMRI studies do not utilize a method of cardiac-related noise reduction, in part because of the lack of information on the regional significance and magnitude of cardiac-related signal variance in the brain. In this paper we present a topographical description of the regions showing significant contributions of cardiac-related signal variance. The results are highly consistent across subjects and suggest that reduced sensitivity due to cardiac-induced noise in the BOLD signal is systematically greater in specific areas, typically near major blood vessels. Significant effects of cardiac-related variability were found on average in 27.5 +/- 8.0% of voxels. Strong influences were found along the vertebrobasilar arterial system near the medial areas of the brain, along the middle cerebral artery near the anterior temporal lobes and in the insula, and along the anterior cerebral artery in the anterior interhemispheric fissure in the medial frontal lobes. Significant effects were also observed in the sigmoid transverse and superior sagittal sinus regions. These results identify regions in which fMRI will have reduced sensitivity due to increased signal variation produced by cardiac pulsatility.