Increased plasma concentration of cyclic GMP in atrial fibrillation.

Plasma concentration of cyclic nucleotides in patients with paroxysmal atrial fibrillation was determined by ultrasensitive radioimmunoassay on the day of attack and also the next day, following recovery to sinus rhythmus. The concentration of cyclic GMP in the plasma of patients with attacks of paroxysmal atrial fibrillation was significantly higher than in those with sinus rhythmus, but no significant difference in plasma concentration of cyclic AMP was observed.