In order to assess concentration of C-reactive protein (CRP) and prevalence of autoantibodies against beta(1)-adrenoreceptors (abeta(1)-AR) in patients with cardiac supraventricular arrhythmias we studied 53 patients with arrhythmias and 20 healthy control subjects. Patients with idiopathic arrhythmias (atrial fibrillation or flutter and atrial tachycardia, n=35) comprised group I. Group II was formed of 15 patients with supraventricular arrhythmias and dilated cardiomyopathy (DCM) or chronic myocarditis. Patients of group III (n=23) had supraventricular arrhythmias and arterial hypertension (AH). CRP concentration was determined by recently developed well standardized high sensitivity method. abeta(1)-AR were detected in blood serum by direct immunoassay. Synthetic fragment containing 26 amino acids of abeta(1)-AR second loop was used as antigen. Patients with supraventricular arrhythmias and DCM or chronic myocarditis had higher median CRP (8.0 mg/1) than patients with idiopathic arrhythmias (0.78 mg/l), with supraventricular arrhythmias and AH (1.57 mg/l), or control group (0.6 mg/l). Groups I, II and III showed similar prevalence of ab1-AR (51.4, 40.0, 52.2%, respectively), that was significantly higher than in control subjects (10%) (p<0.005). These results provide evidence of the possible presence of autoimmune and/or inflammatory processes that may be involved in the genesis of supraventricular arrhythmias.