The effective nuclear interactions in heavy nuclei are discussed on the basis of a semi-phenomenological Hamiltonian for pion-nucleon interactions. Upon application of a canonical transformation the Hamiltonian is diagonalized approximately. The resultant Hamiltonian consists of three parts: (i) the single-particle energy of nucleons, (ii) the energy of the effective meson field, and (iii) the effective interactions between nucleons. The characteristic meson pair term turns out to shorten the range of the two-body correlations and to produce a positive average potential, which may be another cause for the nuclear saturation and may be in favor of the independent-particle behavior.