The purpose of this study is to gather information about the size and shape of patients' hearts in order to design a device.

Correct device design depends on getting good information about the shape and size of the different parts of the heart. Measurements from computed tomography images of hearts will be studied. By looking at measurements from a wide range of patients, an understanding of the differences in the size and shape of the heart chambers will be gained.

Inclusion Criteria:

• Patients deemed suitable for treatment of atrial fibrillation by catheter-based ablation who have received cardiac CT imaging as part of normal care.

Exclusion Criteria:

• Patients who have not received cardiac CT imaging as part or normal care.

Patients with atrial fibrillation who are deemed suitable for treatment of atrial fibrillation by catheter-based ablation.