Cardiovascular disease is the leading cause of death among U.S. adults. Heart failure (HF) is projected to have the largest rise in incidence over the coming decades. Ventricular conduction disorders (including bundle branch blocks, BBB) are prevalent in 10-20% of patients with HF, and in up to 5% of adults in the general population. Notably, BBB can be treated. Cardiac resynchronization therapy (CRT) improves survival and quality of life and reduces HF hospitalizations. The number needed to treat to save a life is 8 for CRT, which is remarkably better than the number for many other HF therapies [26 for ACEi/ARB; 22 for SGLT2i, 23 for ICD]. A 12-lead electrocardiogram (ECG) is routinely used in clinical practice to determine CRT eligibility, based on electrical dyssynchrony criteria of QRS duration and morphology. However, QRS duration and morphology criteria (BBB definitions) of electrical dyssynchrony have limitations, as evident by at least a 30% rate of non-response to CRT. Considering the fact that electrical dyssynchrony predicts CRT response, the development of improved electrical dyssynchrony metrics is crucially important. We designed our study, aiming to refine the electrical dyssynchrony definition. Specific Aim 1. Electrical dyssynchrony and clinically manifested HF. Given the published evidence that two global electrical heterogeneity (GEH) components are risk factors for HF, quantify the risk of incident clinical and subclinical HF using GEH biomarkers and refine the definition of electrical dyssynchrony by combining bundle branch block criteria with 5 GEH metrics. We will test the hypothesis of whether the 5 GEH features are associated with incident HF and whether combining together clinically used (by Strauss et al) BBB criteria and GEH metrics creates a clinically meaningful and powerful definition of electrical dyssynchrony that has a stronger association with incident HF outcomes than traditional definitions. Specific Aim 2. Electrical dyssynchrony and subclinical HF. Determine whether longitudinal changes in the 5 GEH features are associated with longitudinal changes in left ventricular (LV) systolic function, LV filling pressures, and LV dyssynchrony, after adjustment for fixed and time-updated HF risk factors. Compare traditional definitions (QRS duration and morphology) with novel improved definition (see aim 1) that combines QRS & BBB criteria with GEH, regarding their association with LV mechanical function.