Heat capacity is very sensitive to the change in the long- and short-range order effects, which crucially depend on lattice dimensionality and spin-spin interaction. Dimensional crossover is often encountered in actual molecule-based or metal-assembled magnets and thus phase transitions due to the spin ordering may occur at low temperatures even for low-dimensional magnets. The important factor governing the short-range order effect due to magnetic fluctuation is the number of the nearest neighbor magnetic ions as well as the lattice dimensionality.