The superior vena cava (SVC) is a main source of non-pulmonary vein (PV) ectopies that initiate atrial fibrillation (AF). Although the critical role of structural remodeling of the left atrium (LA) in the occurrence of AF was extensively investigated by atrial voltage mapping, that of PVs and the SVC has been less explored. Study subjects comprised 47 patients undergoing catheter ablation of lone AF. During sinus rhythm, PV, SVC, and atrial voltage maps were acquired, and sleeve length of each PV and SVC was determined by an electroanatomical mapping system. The sleeves of the superior PVs were significantly longer than those of the inferior PVs (left superior PV (LSPV): 21 ± 5, left inferior PV: 14 ± 4, right superior PV (RSPV): 19 ± 5, right inferior PV: 15 ± 5, and SVC: 23 ± 10 mm, p < 0.0001). The LSPV sleeve was longer in men than in women (22 ± 6 vs. 19 ± 4 mm, p < 0.05). The sleeve length in the LSPV correlated positively with the body surface area (BSA) (p = 0.003, R = 0.42). Of note, there was a significant correlation in sleeve length between the RSPV and SVC (p < 0.0001, R = 0.64). In conclusion, not right- but left-sided PV sleeves were associated with the BSA of the patients, whereas a structural relation between the right-sided PVs and the SVC was implied based on sleeve mapping. This novel finding may provide mechanistic implications for the development of AF in future studies.