Infarct expansion and extension of the border zone play a key role in the progression of heart failure after myocardial infarction. Increased wall stress, along with complex cellular and extracellular changes in the surviving myocardium, underlie these events and contributes to the adverse cardiac remodeling that drives ventricular dilation and progression of heart failure. Recently, there has been much interest in the development of biopolymers that can be injected into the infarcted myocardium in order to increase its stiffness and thus reduce mechanical stress on the surrounding myocardium. Here we discuss the findings of recent animal studies that have noted improvements in contractile function or cardiac remodeling using either natural or synthetic biomaterials, as well as several that did not. Besides offering physical support to the injured myocardium, injectable biomaterials could also serve the purpose of fostering cardiac repair by functioning as a protective scaffold for stem cell or drug delivery.