BACKGROUND Diastolic heart failure often coexists with atrial fibrillation (AF). Elevated plasma levels of natriuretic peptides are the left ventricular (LV) marker of diastolic dysfunction. OBJECTIVE To evaluate the influence of sinus rhythm restoration on ANP and BNP levels in patients with normal and impaired LV diastolic function. METHODS The study included 42 patients (19 men, 23 women), aged 58.6 +/- 8.2 years with non-valvular persistent AF with preserved LV systolic function who were successfully converted to sinus rhythm by DC cardioversion (CV) and maintained sinus rhythm for at least 30 days. On day 30 following CV in patients with sinus rhythm, Doppler echocardiography was performed to assess LV diastolic function. ECG, echocardiography, ANP and BNP plasma level measurements were made at baseline 24 h before CV and 24 h as well as 30 days after CV. RESULTS The average ANP level in the whole study group during AF was 254.9 +/- 79.9 pg/ml and the average BNP level was 113.6 +/- 49.1 pg/ml. There was an evident decrease in ANP/BNP serum concentration in all the patients after successful DC cardioversion. Measured on the 30th day after CV, ANP and BNP levels were 153.2 +/- 67.9 pg/ml and 61.9 +/- 25.1 pg/ml respectively (p < 0.001). Thirty days after CV normal LV diastolic function was diagnosed in 15 patients and in 27 patients impaired diastolic function: 20 with impaired LV relaxation and 7 with impaired LV compliance. The extent of natriuretic peptides drop was dependent on the LV diastolic function, being more substantial in the subgroup with impaired LV diastolic function. In the subgroup with LV diastolic dysfunction the average ANP serum concentration measured 30 days after conversion was reduced by 111.2 +/- 93.9 pg/ml (37%) (p < 0.001) and BNP level was reduced by 67.5 +/- 36.0 pg/ml (46%) (p < 0.001). In patients with normal diastolic function sinus rhythm restoration significantly influenced ANP level, while having no relevant effect on BNP plasma concentration. The average ANP reduction in this subgroup was 64.4 +/- 71.8 pg/ml (by 38%) and BNP reduction was 11.4 +/- 16.7 pg/ml (by 23%) (NS). CONCLUSIONS The drop in ANP and BNP plasma concentrations after conversion to sinus rhythm in patients with AF depends on the LV diastolic function. Restoration of sinus rhythm is associated with improvement of the heart's haemodynamics, especially in patients with impaired LV diastolic function, which may be inferred from the more pronounced decrease of BNP level after DC cardioversion in this subgroup, as compared to that with normal LV function.