Systems and methods for visualizing ablated tissue are disclosed. In some embodiments, a system for imaging tissue includes a catheter having an expandable balloon at a distal end, an illumination device positioned within the balloon for propagating light from an external light source for illuminating a tissue being treated to excite native nicotinamide adenine dinucleotide hydrogen (NADH) in the tissue, and an imaging device positioned within the balloon for detecting fluorescence from the illuminated tissue, the imaging device being configured to communicate detected NADH fluorescence to an external fluorescence camera.