Display omitted •Subchronic intoxications were induced in male rats by repeated IP injections of lead acetate and/or cadmium chloride.•Right ventricle trabecules and papillary muscle preparations were used for modeling the heart cycle.•Single twitch parameters in trabecules and papillary muscles respond to the intoxications differently.•Intoxications with Pb and Cd led to contra-directional effects on some mechanical parameters and the myosin isoform ratio.•Background administration of bioprotectors attenuated cardio-mechanical effects of Pb + Cd intoxication. Subchronic intoxications induced in male rats by repeated intraperitoneal injections of lead acetate and cadmium chloride, administered either alone or in combination, are shown to affect the biochemical, cytological and morphometric parameters of blood, liver, heart and kidneys. The single twitch parameters of myocardial trabecular and papillary muscle preparations were measured in the isometric regime to identify changes in the heterometric (length-force) and chronoinotropic (frequency-force) contractility regulation systems. Differences in the responses of these systems in trabecules and papillary muscles to the above intoxications are shown. A number of myocardium mechanical characteristics changing in rats under the effect of a combined lead-cadmium intoxication and increased proportion of α-myosin heavy chains were observed to normalize fully or partially if such intoxication was induced against background administration of a proposed bioprotective complex. Based on the experimental results and literature data, some assumptions are suggested concerning the mechanisms of the cardiotoxic effects produced by lead and cadmium.