["Large randomized trials comparing DDD with VVI pacing have shown no differences in mortality, but conflicting evidence exists in regard to heart failure endpoints. Here we evaluated the effect of pacing mode on serum levels of brain natriuretic peptide (BNP) and amino-terminal-proBNP (NT-proBNP). Methods Forty-one patients (age 73 +/- 10 years) with dual-chamber pacemakers were included in a prospective, single-blind, randomized crossover study evaluating the impact of DDD(R)/VDD versus VVI(R) mode on objective and functional parameters. Data were collected after a 2-week run-in phase and after 2 weeks each of VVI(R) and DDD(R)/VDD pacing or vice versa. Results BNP and NT-proBNP levels during DDD(R)/VDD stimulation (151 +/- 131 and 547 +/- 598 pg/mL) showed no change compared with baseline (154 +/- 130 and 565 +/- 555 pg/mL), but a significant 2.4-fold increase was observed during VVI(R) mode [360 +/- 221 and 1298 +/- 1032 pg/mL; P < 0.001 compared with DDD(R)/VDD]. The assessment of functional class, the presence of pacemaker syndrome [49% in VVI(R) mode] and the patients' preferred pacing mode showed significant differences in favour of DDD(R)/VDD pacing."] Does single-chamber ventricular pacing increase markers of left ventricular dysfunction compared with dual-chamber pacing?