This article presents an analytical approach for the quantification of the blood oxygen level dependent (BOLD) effect in the capillary region. The capillary geometry of myocardium is considered. The relaxation rate R*2 is determined as a function of the capillary radius Rc, the intracapillary volume fraction RBV, and the diffusion coefficient D. When the intracapillary volume fraction is small, the approximation R*2 = RBV x tau(-1) x (square root of (1+(taudeltaomega)2)-1) is valid, with the correlation time tau = (Rc2/4D) x (absolute value (ln RBV)/(1 - RBV)). The predictions of this model agree well with numerical simulations and experimental data of others and with data recently measured by our group.