Objective. - Electrical remodeling as well as atrial contractile dysfunction after the conversion of atrial fibrillation (AF) to sinus rhythm (SR) are mainly caused by a reduction of the inward L-type Ca 2 + current (I C a L ). We investigated whether the expression of L-type Ca 2 + -channel subunits was reduced in atrial myocardium of AF patients.Methods. - Right atrial appendages were obtained from patients undergoing coronary artery bypass graft surgery (CAD, n = 35) or mitral valve surgery (MVD, n = 37). Seventeen of the CAD patients and 18 of the MVD patients were in chronic (>3 months) AF, whereas the others were in SR. The protein expression of the L-type Ca 2 + -channel subunits α 1 C and β 2 was quantified by western blot analysis. Furthermore, we measured the density of dihydropyridine (DHP)-binding sites of the L-type Ca 2 + channel using 3 H-PN220-100 as radioligand.Results. - Surprisingly, the α 1 C and the β 2 -subunit expression was not altered in atrial myocardium of AF patients. Also, the DHP-binding site density was unchanged.Conclusion. - The protein expression of the L-type Ca 2 + -channel subunits α 1 C or β 2 is not reduced in atrial myocardium of AF patients. Therefore, the reduced I C a L might be due to downregulation of other accessory subunits (α 2 δ), expression of aberrant subunits, changes in channel trafficking or alterations in channel function.