Aging/metabolism; Matrix Metalloproteinase 9/deficiency; Myocardium/enzymology; Ventricular Dysfunction, Left/prevention & control; Ventricular Function, Left; Age Factors; Aging/pathology; Animals; Blood Pressure; Cell Adhesion Molecules/genetics; Cell Adhesion Molecules/metabolism; Collagen/metabolism; Connective Tissue Growth Factor/genetics; Connective Tissue Growth Factor/metabolism; Diastole; Female; Fibrosis; Gene Expression Regulation; Genotype; Male; Matrix Metalloproteinase 8/genetics; Matrix Metalloproteinase 8/metabolism; Matrix Metalloproteinase 9/genetics; Mice; Mice, Inbred C57BL; Mice, Knockout; Myocardium/pathology; Phenotype; Phosphorylation; Real-Time Polymerase Chain Reaction; Signal Transduction; Smad2 Protein/genetics; Smad2 Protein/metabolism; Systole; Transforming Growth Factor beta/genetics; Transforming Growth Factor beta/metabolism; Ventricular Dysfunction, Left/enzymology; Ventricular Dysfunction, Left/etiology; Ventricular Dysfunction, Left/genetics; Ventricular Dysfunction, Left/pathology; Ventricular Dysfunction, Left/physiopathology