This study investigates the influence of a rapid heat treatment followed by water-quenching on the mechanical properties of Ti6Al4V ELI alloy to improve its strength for use in implants. Prior to the experiment, a dilatometry test was performed to understand the progressive α-to β-phase transformation taking place during heating. The results were then used to carry out heat treatments. Microstructure was analysed using SEM, EBSD, EDX and XRD techniques. Vickers micro-hardness, tensile and high cycle rotating bending tests were used to analyse the influence of the $\alpha'$-phase fraction on the strength of the studied alloy. Results show that this process can provide a Ti6Al4V ELI alloy with a better Yield Strength (YS)/uniform deformation (εu) ratio and improved high cycle fatigue strength than those observed in the current microstructure used in medical implants. Lastly, cytotoxicity tests were performed on two types of human cells, namely MG63 osteoblast-like cells and fibroblasts. The results reveal the non-toxicity of the heat-treated Ti6Al4V ELI alloy.