The risk of developing atrial fibrillation is increased in patients with metabolic syndrome, but atrial conduction properties are uncharacterized in patients who have metabolic syndrome without atrial arrhythmia. We used tissue Doppler imaging to evaluate intra- and interatrial synchronicity in such patients. The imaging was performed in 145 patients with metabolic syndrome and 110 controls. Atrial synchronicity was determined from the intervals between the onset of the P-wave to the onset of the A-wave at the left atrial free wall (P-LA), interatrial septum (P-IAS) and right atrial free wall (P-RA). Intra-atrial synchronicity was defined as the differences between P-IAS and P-RA (RA synchronicity) and between P-LA and P-IAS (LA synchronicity). Interatrial synchronicity was defined as the difference between P-LA and P-RA. P-LA and P-IAS were significantly prolonged in the metabolic syndrome group relative to the control group (P-LA: 64.34+/-13.99 vs. 55.35+/-12.67, P<0.001; P-IAS: 36.49+/-12.39 vs. 31.55+/-11.61, P=0.001), whereas P-RA showed no difference. As a result, this caused impaired intra- and interatrial synchronicity in patients with metabolic syndrome. Stepwise multivariate linear analysis revealed insulin resistance as an independent predictor of impaired intra- and interatrial synchronicity. Subgroup analysis indicated that there was no difference in atrial asynchrony between non-hypertensive and hypertensive subgroups in metabolic syndrome patients. In conclusion, patients with metabolic syndrome without atrial arrhythmia have impaired intra- and interatrial synchronicity. Insulin resistance has an important role in impaired atrial conduction in these patients.