SUMMARYTo determine whether plasma ANP and/or BNP levels can be used to detect limitations in daily physical activity after pacemaker implantation, we measured plasma ANP and BNP levels at a pacemaker follow-up clinic in 56 patients (62±15 yrs, 2AAI, 9VVI, 34DDD, 7VDD and 4 rate-responsive modes). daily physical activity evaluated by a specific activity scale questionnaire (METs) and VO 2 max obtained by expired gas analysis during ergometer exercise.A very clouse correlation (n=6, r=0.89, p<0.05) was obseved between. ANP in patients with daily physical activity class III (2-4 METs, n=21) was significantly higher than class II (5-6 METs, n=23, p<0.01) and class I (>7 METs, n=8, p<0.01), while BNP in class III patients was significantly higher than in class II (p<0.0001) and class I (p<0.0001) patients. Significant correlations between daily physical activity and BNP (r=-0.64, p<0.0001) and ANP (r=-0.43, p<0.001) were observed. Physiological pacing mode did not necessarily offer a better profile for BNP levels compared with non-physiological pacing modes. Patients with ventricular pacing (wide QRS: VDD, RR-VVI and VVI) showed significantly high ANP (p<0.01) and BNP (p<0.01) levels compared with those in patients with atrial pacing (narrow QRS: AAI and RR-AAI). During exercise, plasma catecholamines and ANP levels were significantly elevated, however, BNP levels, which were already elevated at rest, did not change significantly, and reflected a limitation of daily physical activity. The present study revealed that 37.5% of the patients displayed an elevation in BNP and this was judged to be a limitation of physical activity class III being equivalent to NYHA II or more. Elevated resting BNP levels reflected a limitation in daily physical activity in these patients. These findings suggested a third condition for physiological pacing-synchronization of ventricular contraction (narrow QRS pacing) -in addition to the two conventional conditions of atrioventricular synchrony and rate-responsiveness. (Jpn Heart J 2001; 42: 471-482) Key words: Physiological pacing, Brain natriuretic peptide, Congestive heart failure, Physical activity, Dyssynchronization WE have reported that the electrophysiological consequences of the heart following pacemaker implantation are closely related to the cardiodynamic and neuFrom