Equation of motion coupled-cluster calculations (EOM-CCSD) have been performed to obtain N-15-N-15 and O-17-O-17 coupling constants ((2h)J(X-X)) across N-H+-N and O-H+-O hydrogen bonds in a series of protonated dimers. (2h)J(X-X) values are dominated by the Fermi-contact term and are distance dependent. Large coupling constants are associated with symmetric hydrogen bonds, short hydrogen bond distances, and low electron densities on the hydrogen-bonded proton, and are not related to the binding energies of these complexes. The magnitudes of coupling constants do not appear to be related; to the nature of the covalent bonding of the hydrogen-bonded nitrogen and oxygen atoms, although this bonding indirectly determines the coupling constant by determining the N-N or O-O distance. Complexes with sp(2)-hybridized oxygens are more sensitive to the trans or cis orientation of the hydrogen-bonded pairs than are the corresponding nitrogen complexes. One-bond coupling constants ((1h)J(X-H)) are greater than two-bond couplings ((2h)J(X-X)) in complexes with symmetric hydrogen-bonds, but (1)J(N-H) is greater than (2h)J(N-N) which is greater than (1h)J(N-H) for nonsymmetric hydrogen bonds. When reduced coupling constants are used for comparison, K-2h(X-X) is always greater than K-1(X-H), which is greater than K-1h(X-H).