Microreentrant tachycardias are well described and are thought to be responsible for a small proportion of atrial tachycardias post–atrial fibrillation (AF) ablation. However, because of the small size of these reentrant circuits and the poor spatial resolution of conventional mapping tools, they have not previously been mapped accurately in vivo in humans and have therefore been difficult to distinguish from nonreentrant focal tachycardias. The newly developed Rhythmia electroanatomic mapping system allows for the rapid creation of activation maps of ultra-high resolution. In this case report, we provide the first images of a microreentrant atrial tachycardia circuit in a post-AF setting, mapped with the high-resolution Rhythmia mapping system.