Potassium, sodium, calcium and magnesium were determined in the plasma and erythrocytes of 129 patients with toxic goiter; phasic structure of the systole of the left ventricle was studied as well. Correlation coefficients between the indices of electrolyte metabolism and the phasic structure of the systole were studied for the purpose of ascertaining the relation between the changes in the contractile function of the myocardium and the electrolyte level. The most significant correlative association was revealed between the electrolytes and the period of ejection, the mechanical and the acoustic systoles.