Plasma from patients with inflammatory dilated cardiomyopathy (DCMi) contains antibodies against cardiac antigens. Removal of immunoglobulin G (IgG) from plasma of DCMi patients by immunoadsorption improves hemodynamic parameters in many patients. The aim of the current study was to test effects of immunoglobulins from DCMi patients on cardiac L-type calcium channels. Ca2+ currents were recorded from rat cardiomyocytes and 150 mg/l or 300 mg/l IgG applied. At 300 mg/l the IgG fraction of a DCMi patient reduced the Ca2+ current amplitudes of the test cells in average by 35 % compared to the value in external solution (n=7 cells). IgG from two other patients showed a similar but minor effect. The kinetics of Ca2+ currents was markedly changed by DCMi-IgG. The time constants of inactivation of current transients decreased from 67 ± 8 ms to 43 ± 6 ms in the presence of 300 mg/l DCMi-IgG (n=7). Both effects were nearly reversible after wash out. IgG fractions from three healthy donors showed only slight inhibitory effects on Ca2+ currents analysed under the same conditions. We conclude that immunoglobulins from DCMi patients can interfere with cardiac calcium channels. This may contribute to the negative inotropic effect of immunoglobulins on cardiac muscle observed in these patients. (Supported by DFG, SFB-TR 19, project C2)