The significance of left ventricular false tendon and right atrial anomalous muscular band has been previously reported. As well as in the right atrium, anomalous muscular band is sometimes observed in the left atrium. To evaluate the prevalence and clinical significance of the left atrial anomalous band, a clinico-pathologic study was performed among 1,100 autopsies over 60 years. The following results were obtained: (1) Pathologically, the incidence of the left atrial anomalous band was 2% (22 cases among 1,100 autopsies). The anomalous band connected the left atrial side of fossa ovalis with the other areas of left atrial endocardium in most of the cases (19 cases). The cases with the bands had Chiari's network and patent foramen ovale at the same time more frequently than those without the bands (Chiari's network: 27% vs 8%, p < 0.01, patent foramen ovale: 23% vs 8%, p < 0.05). Microscopically, the anomalous band was composed of fibrous and muscular tissues. (2) Clinically, premature atrial complex was more frequently observed among the cases with left atrial anomalous bands than those without the bands (41% vs 11%, p < 0.01). In conclusion, left atrial anomalous band seemed to be one of congenital abnormalities which was associated with Chiari's network and patent foramen ovale in origin, and might be one of the causes of supraventricular arrhythmias.