Dilated cardiomyopathy remains a leading cause of morbidity and mortality, consuming a major share of health care resources. While the disease is initiated by a primary insult to the myocardium, the sustained inability of the heart to adequately provide systemic blood flood soon leads to neurohumoral stimulation that can amplify cardiac dysfunction. We recently reported that combining exogenous angiotensin-II (A-II) infusion, even at normotensive doses, with short-term (48 hour) tachycardia pacing leads to accelerate progression of cardiac dysfunction, most notably in diastole. Neither stimulus alone was sufficient to induce similar dysfunction. This synergy was associated with alterations in the extracellular matrix with increases in metalloproteinase (MMP) abundance and activity. We hypothesize that cross-talk between adrenergic and A-II systems and evolving cardiac dysfunction play a major role in accelerating functional deterioration, and that MMP activation is an important contributor to this process. We propose that MMP activation contributes to evolving cardiac dysfunction at chamber and myocyte levels by adversely altering the biochemical and physical extracellular environment. The studies outlined in this project are performed using a hybrid canine model of cardiac dysfunction based on combining selective neurohumoral activation with/without specific receptor of MMP inhibitors. and 48-72 hours of rapid ventricular pacing. This duration of pacing itself generates moderate systolic dysfunction accompanied by depressed adrenergic signaling and abnormalities of excitation-contraction coupling, but with minimal changes in diastolic stiffness. By separately providing neurohormone stimulation and selective receptor blockade (or MMP inhibition), the precise role and interaction of each factor is more precisely determined. The specific aims define the signaling crosstalk (i.e. beta1, beta2, AT1) for AII-modulation of failure exacerbation, and th4e nature and mechanisms by which MMP activation contributes to this interaction. We test the hypothesis that A-II mediated MMP activation alters cardiac interstitial composition, increasing myocardial hormone and cytokine levels, and generating an oxidating environment. Chronic sampling of cardiac lymph is employed for these studies. We will determine how neurohormonal activation ans associated MMP changes influence basal and hormone-stimulated myocyte electrophysiologic behavior, focusing on mechanisms underlying action potential prolongation and altered calcium Ca2+ signaling. Lastly, we test the relation between myocyte electrophysiological and functional changes and the activation of MMPs and matrix remodeling in end-stage failing human hearts. Data are also obtained from patients treated with chronic ventricular assist devices that unload the heart and can reverse chamber remodeling. These studies will provide critically important novel insights regarding the interaction of MMPs and the heart, neurohormonal regulation of MMPs in heart failure, and the mechanisms by which these changes mediate failure progression.