A system and method for characterizing the atrial wall of the heart is provided. The characterization of the atrial wall can be used for a variety of diagnostic and therapeutic purposes. For example, it can be used to detect precursors to various types of hear disease, such as atrial fibrillation. In one embodiment, the system and method is used to determine a likelihood of fibrosis in the atrial wall. Furthermore, the system and method can detect changes in atrial wall fibrosis that can indicate a continuing degradation in the atrial wall health and an increasing likelihood of atrial fibrillation. In another embodiment, the system and method is used to determine if electrical instability exists in the atrial wall.