The theory of heterogeneous condensation of vapor was elaborated for a case of practical interest: macroscopic condensation nuclei and the gradual creation of the metastable state in vapor. The reference value was found for ideal supersaturation, which ensures external control over the development of the condensation process. All the principal kinetic characteristics of heterogeneous nucleation of supercritical droplets in vapor were found in terms of the external parameters of the theory, which are determined by the properties of the vapor and the liquid condensing from it, by the dimensions of the condensation nuclei and their initial concentration, and by the rate of the external increase in ideal supersaturation. The conditions of applicability were formulated for the suggested theory. Fast convergence of the iterative method of contractive approximations in the determination of the total number of supercritical droplets originating per unit volume of the vapor-gas medium was demonstrated. The theory was shown to be directly generalizable for the case of polydisperse macroscopic condensation nuclei.