A method and apparatus for forming a lesion in tissue along a desired
ablation path with treating a body tissue in situ (e.g., an atrial tissue
of a heart to treat) atrial fibrillation include a lesion formation tool
including is positioned against the heart surface. The lesion formation
tool includes a guide member having a tissue-opposing surface for
placement against a heart surface. An ablation member is coupled to the
guide member to move in a longitudinal path relative to the guide member.
The guide member includes a track. A carriage is slidably received with
the track. The ablation member is secured to the carriage for movement
therewith. The guide member includes a visualization component.