The aim of this study was to estimate the values of morphological traits of myocardium in American minks. The study was conducted on 342 male mink hearts and 416 female mink hearts. Mink coat coloration resulting from mutation or crossbreeding of mutational variants with each other and sex were assumed as a source of variation. Carcass, lung and heart weights, heart height, width, depth and circumference, as well as left and right ventricular wall weights and thickness at two locations were determined. The values of 10 indices characterising the relative size of the heart were estimated. The results showed no normal distribution of the heart traits examined. The greatest average heart weight was characteristic of male mutational colour variant minks (17.40 +/- 2.34 g). These hearts were heavier by more than 8 % than those of male standard colour variant minks. The hearts of male mutational colour variant minks were characterised by the greatest left and right ventricle weights (P <= 0.01) compared to those of male standard colour variant minks, in which in turn the greatest left and right ventricle wall thickness was larger than that in standard colour variant minks. It was found that a greater difference calculated between mean left ventricle wall thickness and mean right ventricle wall thickness in standard colour variant minks may provide more evidence of its adaptation to a greater effort, referring thus to their evolutionary history than to the occurrence of signs of multistage myocardial hypertrophy.