Increasing demand for quantitative diffusion MRI in biomedical research necessitates a reevaluation of potential sources of artifact. While cardiac pulsation-induced effects have been reported previously, their quantitative characterization under standard acquisition protocols remains outstanding. To determine whether practical data quality improvements merit the use of cardiac gating, the maximum effects induced in apparent diffusion coefficient, fractional anisotropy, and mean diffusivity measurements were quantitatively estimated via measurements and bootstrapping simulations. In apparent diffusion coefficient time courses, cardiac pulsation effects were measured to occupy approximately 6% of the heartbeat duration, with considerable intersession differences in effect magnitude. Bootstrapping revealed overestimations in fractional anisotropy up to 0.26, and mean diffusivity up to 0.19 x 10(-3) mm(2) sec(-1) without gating compared to 0.072 (fractional anisotropy) and 0.043 x 10(-3) mm(2) sec(-1) (mean diffusivity) in the same gated simulation. However, while cardiac pulsation may thus impair the quantification of fractional anisotropy and mean diffusivity in some individuals, our data suggested negligible effects in group studies.