b 1 -AR Ser49Gly genotype was associated with mean heart rate and SDNN with borderline significance (Table 1 ; p = 0.087 and p = 0.064, respectively). No statistical association was found between b 2 -AR Gln27Glu genotype and HRV indices ( Table 2) . For the b 2 -AR Arg16Gly genotype (Table 3) , a significant codominant association was found with LF% (F = 3.636, p = 0.028) and the non-randomness index derived from the IBS method (F = 5.642, p = 0.004). Multiple comparisons showed that LF% was significantly lower in homozygous Arg16 carriers compared to subjects with the Arg16/Gly16 genotype (p = 0.016), but not to homozygous Gly16 carriers (p = 0.985). Likewise, a significantly lower non-randomness index was found in homozygous carriers of the Arg16 allele (p = 0.016) compared to subjects heterozygous for Arg16/Gly16 (p = 0.001), and a borderline significance was seen in the comparison to homozygous Gly16 carriers (p = 0.057).