Tissue inhibitor of metalloproteinases 4 (TIMP4) is expressed highly in heart and found dysregulated in human cardiovascular diseases. It controls extracellular matrix remodeling by inhibiting matrix metalloproteinases (MMPs) and is implicated in processes including cell proliferation, apoptosis, and angiogenesis. Timp4-deficient mice (Timp4 ؊/؊ ) were generated to assess TIMP4 function in normal development and in models of heart disease. We deleted exons 1-3 of the Timp4 gene by homologous recombination. Timp4 ؊/؊ mice are born healthy, develop normally, and produce litters of normal size and gender distribution. These mice show no compensation by overexpression of Timp1, Timp2, or Timp3 in the heart. Following cardiac pressure overload by aortic banding, Timp4 ؊/؊ mice have comparable survival rate, cardiac histology, and cardiac function to controls. In this case, Timp4 deficiency is compensated by increased cardiac Timp2 expression. Strikingly, the induction of myocardial infarction (MI) leads to significantly increased mortality in Timp4 ؊/؊ mice primarily due to left ventricular rupture. The post-MI mortality of Timp4 ؊/؊ mice is reduced by administration of a synthetic MMP inhibitor. Furthermore, combining the genetic deletion of Mmp2 also rescues the higher post-MI mortality of Timp4 ؊/؊ mice. Finally, Timp4 ؊/؊ mice suffer reduced cardiac function at 20 months of age. Timp4 is not essential for murine development, although its loss moderately compromises cardiac function with aging. Timp4 ؊/؊ mice are more susceptible to MI but not to pressure overload, and TIMP4 functions in its capacity as a metalloproteinase inhibitor after myocardial infarction.Tissue inhibitors of metalloproteinases (TIMPs) 5 comprise a family of four endogenous inhibitors. Classically, matrix metalloproteinases (MMPs) and TIMPs are known as important regulators of extracellular matrix turnover during physiologic and numerous pathologic processes. Several other functions also have been ascribed to MMPs, many of which extend to their inhibitors (1). TIMPs also exhibit functions that appear to be independent of their metalloproteinase inhibitory capacity (2).TIMP4 is the most recently discovered member of the TIMP family. It inhibits several soluble MMPs (types 1, 2, 3, 7, 8, 9, 12, 13, 19, and 26) and membrane-type MMPs (MT1, MT2, and MT3) (3-7). TIMP4 also inhibits a disintegrin and metalloproteinase (ADAM) 28 and ADAM33 (7) but not ADAM10 (which is inhibited by TIMP1 and TIMP3) or ADAM17 (which is inhibited only by TIMP3) (2,7,8). Inhibition of the ADAMTS (ADAM with thrombospondin motifs) family by TIMP4 has not yet been reported. Although Timp genes 1, 2, and 3 are widely expressed, the Timp4 gene exhibits a restricted tissue expression pattern, with the highest expression in the heart, followed by brain, ovary, and skeletal muscle, and TIMP4 protein is detectable in the serum (9 -11). Several lines of evidence suggest a specific role in cardiovascular pathology: Timp4 is induced following endothelial injury of rat carotid art...