Effect of the lipid peroxidation (LP) on the Ca2+-transport and the effect of different Ca2+-concentrations on the LP activation were studied in microsomes and mitochondria of the heart. A slight accumulation of LP-products in the microsomal fraction results in a complete inhibition of the membrane calcium-transport activity. Preliminary administration of antioxidants (4-methyl 2,6-ditretbutylphenol and alpha-tocopherol) prevents both the accumulation of LP-products and damage of the Ca2+-transport system. Calcium at 10(-6) M to 5 X 10(-5) M concentrations stimulates LP and while being increased to 2 X 10(-3) M it inhibits LP. The data obtained evidence an interrelation between alterations of the Ca2+-concentrations and LP activation in cardiomyocytes.