The invention is directed to tissue-engineered biografts, methods for preparing the biografts of the invention, and methods for repairing a damaged myocardium in a mammal. The methods of the invention can include providing a three-dimensional porous polysaccharide matrix; introducing mammalian cells into said matrix; growing said cells in said matrix in vitro, until a tissue-engineered biograft is formed; and transplanting the tissue-engineered biograft onto myocardial tissue or myocardial scar tissue of said mammal. The tissue-engineered biograft of the invention can form a contracting tissue. The methods of the invention can optionally include removing scar tissue or dead tissue from the site of implantation prior to transplanting the biograft.