Hot -Ion H-modes (H-I) are the discharges which produce the highest fusion performance on JET. The main MHD features observed during such discharges are small ELMs at the L-to-H transition, a sawtooth usually within the first 300ms, low 'n' core modes rotating with the bulk plasma ions, outer modes (OM) ~0.9-1.3 s. into the H-I discharge and a Giant ELM at the end of the high performance phase after ~1.3-1.8 s. The performance of a H-I discharge for the same current and power is primarily determined by the timing and amplitude of the outer modes and giant ELM. These two modes are regarded as edge phenomena, yet a global loss in performance occurs. Little change in MHD was observed when going from D-D to D-T plasmas.