The current invention discloses a method for treating infracted/ischemic injury to a myocardium by injecting a substance into the myocardium. The injected substance helps to prevent negative adaptive remodeling by providing mechanical reinforcement or mechanical reinforcement combined with biological therapy. A number of substances for injection are disclosed, including multi component substances such as platelet gel, and other substances. The substances disclosed may contain additives to augment/enhance the desired effects of the injection. The invention also discloses devices used to inject the substances. The devices can include means for ensuring needles do not penetrate beyond a desired depth into the myocardium. The devices can also include needles having multiple lumens such that the components of the platelet gel will be combined at the injection site and begin polymerization in the myocardium.