  We report synthesis and magnetic properties of quasi-one-dimensional
spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain compound
BaNa$_2$Cu(VO$_4$)$_2$. This orthovanadate has a centrosymmetric crystal
structure, $C2/c$, where the magnetic Cu$^{2+}$ ions form spin chains. These
chains are arranged in layers, with the chain direction changing by 62$^0$
between the two successive layers. Alternatively, the spin lattice can be
viewed as anisotropic triangular layers upon taking the inter-chain
interactions into consideration. Despite this potential structural complexity,
temperature-dependent magnetic susceptibility, heat capacity, ESR intensity,
and NMR shift agree well with the uniform spin-$1/2$ Heisenberg chain model
with an intrachain coupling of $J/k_{\rm B} \simeq 5.6$ K. The saturation field
obtained from the magnetic isotherm measurement consistently reproduces the
value of $J/k_{\rm B}$. Further, the $^{51}$V NMR spin-lattice relaxation rate
mimics the 1D character in the intermediate temperature range, whereas magnetic
long-range order sets in below $T_{\rm N} \simeq 0.25$ K. The effective
interchain coupling is estimated to be $J_{\perp}/k_{\rm B} \simeq 0.1$ K. The
theoretical estimation of exchange couplings using band-structure calculations
reciprocate our experimental findings and unambiguously establish the 1D
character of the compound. Finally, the spin lattice of BaNa$_2$Cu(VO$_4$)$_2$
is compared with the chemically similar but not isostructural compound
BaAg$_2$Cu(VO$_4)_2$.
