Abstract: Twenty-eight patients with auricular fibrillation （AF） were investigated for plasma trial natriuretic peptide （ANP） during and after their paroxysms. Plasma levels of ANP were ignificantly higher during AF attacks than that during silent periods （609.5±40.6 vs 397.4±1.2pg/ml, P＜0.05）. At the same time, serum ANP concentration and urine ANP elimination were lso studied for searching simpler methods for clinical use. The study also gave higher figures uring AF episodes. Increased plasma ANP in patients with AF, in spite of the length of course r the condition of cardiac function, indicates that arrhythmias may play an important role in NP synthesis and secretion. The mechanism may be that the increase is not only affected by ntracavitary pressure （present also in heart failure） but also by the degree of atrial wall tress and the wall elasticity.