Disclosed are compositions and methods for method of treating a subject having reduced cardiac function or cardiac disease by administering adult bone marrow-derived stem cells to an individual. In some embodiments, the subject is a myocardial infarction patient or congestive heart failure patient. These cells can be administered as a liquid injectable or as a preparation of cells in a matrix which is or becomes solid or semi-solid. The cells can be genetically modified to enhance myocardial differentiation and integration. Also disclosed is a method for replacing cells ex vivo in a heart valve for implantation.