A medical ablation system (10) includes an elongate element (12) to be inserted endoluminally into a patient's vessel (140) and includes at its distal end (14) a pre-heating element (22) and an ablation element (20, 210, 310, 410). The system (10) provides pre-heating of, for example, blood to a first threshold temperature above body temperature but below ablation temperature； and then a second heating stage provided by the ablation element (20, 210, 310, 410). Preheating reduces the amount of energy required to effect ablation, resulting in more focussed embolization with a higher proportion of energy delivered to the area in a more controlled manner. The arrangement can reduce the amount of damage to surrounding tissues and organs.
