Background: Heart failure with a preserved ejection fraction (HFpEF) is a leading cause of mortality and morbidity that, to date, remains poorly characterized. Recent evidence suggests that HFpEF is associated with significant systolic dysfunction despite relatively normal electrical function. This study aims to explore electro-mechanical dysfunction (EMD) across HFpEF with EF>35%. Methods: We studied clinical features, electrical and mechanical function (using ECG and Echo with Tissue Doppler, TDI) in HF patients: 25 with EF between 35–50% (Mid EF); 30 with EF>50% (High EF); and 10 healthy controls (Control). EMD was measured using Ts, defined as time from QRS onset to peak systolic velocity from TDI for 12 myocardial segments across the left ventricle. EMD was studied at baseline and after a mild exercise protocol. Results: The Mid and High EF groups had significantly longer mean EMD (197±28 and 213±24ms), at baseline, compared to Control (146±13ms, p<0.01). Post-exercise, mean EMD in Control and High EF significantly shortened (114±16 and 199±29ms, respectively, p<0.01), relative to baseline values, but not the Mid EF group (192±33ms). Regional EMD analysis across the 12 segments revealed that Ts in the Mid EF group was significantly and consistently lengthened (max segmental delay=33ms), indicating the presence of global EMD. In contrast, in the High EF group, Ts was significantly lengthened only in lateral and posterior segments (max segmental delay=107ms), indicating the presence of regional EMD. Compared to control values, EMD in the Mid EF group was associated with larger QRS width (99±19 vs. 85±8ms) and diastolic diameter (57±8 vs. 47±5 mm, p<0.05) but not in the High EF group (92±13ms and 46±4 mm, respectively). Nonetheless, regional EMD in the High EF group was significantly different than Control despite the narrow QRS and small chamber. The EMD profile for Mid and High EF was not altered post-exercise. Conclusion: EMD plays a significant role in the cardiac dysfunction observed in HFpEF with mechanistically different properties across HF groups when segmented by EF. In the Mid EF group, global EMD is a dominant dysfunction and is associated with electrical delays and larger ventricular dimensions. In the High EF group, regional EMD is a dominant dysfunction which involves delayed mechanical activation at lateral and posterior segments only. Furthermore, mild exertion impacts EMD in the High EF group only.