Background: Atrial fibrillation (AF) is the most common serious aberrant cardiac arrhythmia. Many AF patients present with symptoms of dyspnea and fatigue, but have normal left ventricular ejection fraction (LVEF). Purpose: To determine if measurements of global longitudinal strain (GLS) and strain rate are feasible in patients with AF and examine if the arrhythmia is associated with abnormal left ventricular (LV) strain and strain rate independent of age, sex, heart rate, LVEF and LV mass. We hypothesized that AF independently reduces ventricular systolic performance. Methods: The study was conducted as a retrospective analysis of images from 150 randomly selected patients with AF compared to an equal number of subjects with sinus rhythm (SR) matched for age, sex, heart rate, LVEF and LV mass. Half of the patients had normal LVEF (LVEF ≥ 50%) and half had reduced LVEF (LVEF < 50%). GLS and strain rate were measured in each group, as were quantitative LV volumes and standard systolic and diastolic parameters. Results: GLS was significantly inferior in the patients with AF compared to subjects with SR, both in the overall population (-12.25 ± 4.1% vs. –16.13 ± 4.7%, p<0.0001), in patients with normal LVEF (-14.41 ± 3.9% vs. –19.42 ± 3.1%, p<0.0001) and in patients with reduced LVEF (-10.10 ± 3.1% vs. –12.85 ± 3.5%, p<0.0001). Conclusion: Patients with AF have significantly inferior values of GLS compared to similar patients with SR independent of age, sex, heart rate, LVEF and LV mass.