Provided are pharmaceutical compositions that include a pharmaceutically acceptable carrier and isolated post-natal cardiac progenitor cells (CPCs) and/or progeny cells thereof that are SSEA3-positive and c-kit-negative. Also provided are methods for preparing cells capable of repairing damaged myocardium, methods for isolating populations of SSEA3-positive/c-kit-negative CPCs from cardiac tissue samples, methods for preparing an isolated cell population enriched in post-natal SSEA3-positive/c-kit-negative CPCs, therapeutic methods for using the presently disclosed cells and populations of cells to treat subjects in need thereof, and cell cultures that contain the presently disclosed cells and populations of cells.