In our previous work we have shown that the age-dependent decrease in the magnetosensitivity of heart muscle hydration is accompanied by a dysfunction of the Na+/K+ pump. The reciprocal relation between the Na+/K+ pump and Na+/Ca2+ exchange in development was suggested as a possible pathway for the age-dependent decrease in the magnetosensitivity of heart muscle hydration (water content). Because high and low affinity ouabain receptors in cell membranes are involved in Na+/Ca2+ exchange and Na+/K+ pump functions, respectively, the effect of a 0.2 T static magnetic field (SMF) on dose-dependent, ouabain-induced hydration and [3H]-ouabain binding with heart muscle tissues in young, adult and older rats was studied. Three populations of receptors in membranes with high (10−11–10−9 M), middle (10−9–10−7 M) and low (10−7–10−4 M) affinity to [3H]-ouabain were distinguished, which had specific dose-dependent [3H]-ouabain binding kinetics and effects on muscle hydration. The magnetosensitivity of [3H]-ouabain binding kinetics with high affinity receptors was prominent in all the three age groups of animals, while with low affinity receptors it was more expressed only in the young group of animals. All three types of receptors that caused modulations of muscle hydration were age dependent and magnetosensitive. Based on the obtained data we came to the conclusion that heart muscle hydration in young animals is more magnetosensitive due to the intense expression of high affinity ouabain receptors, which declines with aging. Bioelectromagnetics 34:312–322, 2013. © 2012 Wiley Periodicals, Inc.