Physiological variables must often be scaled for body size differences to permit meaningful comparisons between subjects or groups. This study aimed to determine the proper relationship between body dimensions and left ventricular mass (LVM) via allometric scaling (AS) in 142 subjects (78 males, 64 females; ages 18-40). A cubic formula was used to estimate LVM from wall thicknesses and left ventricular internal dimensions derived from M-mode echocardiography. Fat free mass (FFM) was predicted from anthropometry.“Best compromise” allometric equations (y = a·xb) revealed a common body mass (BM) exponent of 0.78 (95% CI, 0.65-0.91). The widely adopted ratio scaling (RS) method assumes that the exponent b= 1. In this sample, use of RS would penalize heavier subjects by overcorrecting for BM. The equivalent mean FFM exponent of 1.07 was not different from unity (95% CI, 0.92-1.22). Hence, RS using BM would appear to penalize those subjects who are heavier owing to excess fat not excess FFM. Gender differences in LVM were 70, 44, and 18%, for absolute values per BM0.78 and per FFM1.07, respectively (P < 0.05). This reveals quantitative differences in heart size independent of body dimensions. We conclude that sample specific AS permits meaningful intersubject or intergroup comparisons.