This paper presents the hardware implementation of a wavelet based event detector for cardiac pacemakers. A high level energy estimation flow was applied to evaluate energy efficiency of standard-cell based designs, over several CMOS technology generations, from 180 to 65 nm, operated in the sub-threshold domain. The simulation results indicate a 65 nm low-leakage high-threshold (LL-HVT) CMOS technology as the favourable choice. Accordingly, the design was fabricated in 65nm LL-HVT CMOS. Measurements validate the simulation results and prove that the circuit is fully functional down to a supply voltage of 250mV. At the energy minimum voltage of 320mV the circuit dissipates 0.88 pJ per sample at a clock rate of 20 kHz.