Spherical nanoparticles (NP) of cadmium and lead sulfides (dia.37 ± 5 nm and 24 ± 4 nm, respectively) turned to be cytotoxic for HL-1 cardiomyocytes as illustrated by ATP-dependent luminescence reduction. It was revealed, that CdS-NP affect in a greater degree than PbS-NP. In view of the same dose range, CdS-NP decreased the amount of calcium spikes. Small PbS-NP doses showed the same effect. Besides cell hypertrophy due to certain CdS-NP and PbS-NP impact, doses leading to cardiomyocyte decrease were revealed. In order to correspond with the following three results, both monotonic «dose-response» functions (properly approximated by the hyperbolic function) as well as different variants of non-monotonic ones were deduced by us, for which adequate mathematical expressions through modifying certain hormesis models are to be had in literature. Evidence-based analysis involving response surface linear model as well as a cross term, acknowledged a new support to the formerly inflexible rule stating that the diversity kinds of combined action, typical for the same damaging agents’ pair is of the fundamental propositions in the general theory of combined toxicity.