BACKGROUND The shape of the left atrial appendage (LAA) might affect thrombus formation. The chicken wing-type LAA (CW) has been reported as unlikely to influence stroke events in atrial fibrillation (AF) patients, so we investigated whether LAA shapes could influence LAA function. RESULTS We studied 102 patients (64 men, age 65±9 years) who underwent transthoracic echocardiography, transesophageal echocardiography (TEE), and cardiac computed tomography prior to catheter ablation (CA) for AF. LAA morphology were classified into 2 types: (1) CW: LAA with a bend in its shape and (2) non-CW type (NCW): LAA without any bends. All patients were classified into these groups using a cutoff value of LAA flow velocity (LAAFV). Patients with LAAFV <35 cm/s were classified as the low LAAFV group (Low FV, n=37). The patients with LAAFV >35 cm/s were classified as normal LAAFV group (Normal FV, n=65). The NCW type was detected in 25/102 patients (25%). In multivariate analysis, the patients with Low FV were associated with NCW type (P=0.0429, odds ratio [OR] 9.664, 95% confidence interval [CI] 1.075-86.900) and higher B-type natriuretic peptide (BNP) (P=0.0350, OR 1.012 for each 1 pg/ml increase in BNP, 95% CI 1.001-1.022). CONCLUSIONS The NCW-type LAA and higher BNP were associated with lower LAAFV. One reason for the frequent cardiogenic stroke in patients with the NCW-type LAA may be the lower LAAFV.