Cardiac ablation instrument

A hand held cardiac ablation instrument comprising:

• a slidably disposed light transmitting optical fiber;
• a housing in the shape of an open toroidal loop having a first end adapted to receive the slidably disposed light transmitting optical fiber;
• and
• at least one diffuser chamber coupled to the fiber within the housing.

A method of ablating cardiac tissue, comprising:

• positioning a device in proximity to a target region of cardiac tissue, the device having a light diffusing element coupled to a source of photoablative radiation and configured in a toroidal shape to emit an arcuate pattern of radiation;
• applying the device to the target region to induce an curvilinear lesion;
• moving the device to a second position;
• reapplying the device to the target region to induce a second curvilinear lesion;
• repeating the steps of positioning and applying until the lesions are joined together to create a composite circumferential lesion.