Influence of mercury and selenium chemistries on the progression of cardiomyopathy in pygmy sperm whales, Kogia breviceps

► More than half of stranded pygmy sperm whales exhibit signs of cardiomyopathy. ► Hg and Se balance and oxidative stress may influence progression of cardiomyopathy. ► Adults have significantly greater Hg:Se liver molar ratios than younger age classes. ► Hg:Se molar ratios were greater in males and increased with heart disease progression. ► Protein oxidation was greater in males and increased with heart disease progression.