['Cardiac progenitor cells are important for maintenance of myocardial structure and function, but molecular mechanisms governing these progenitor cells remain obscure and require elucidation to enhance regenerative therapeutic approaches.', 'To understand consequences of stem cell antigen-1 (Sca-1) deletion on functional properties of c-kit+ cardiac progenitor cells and myocardial performance using a Sca-1 knock-out/green fluorescent protein knock-in reporter mouse (ScaKI).', 'Genetic deletion of Sca-1 results in early-onset cardiac contractile deficiency as determined by echocardiography and hemodynamics as well as age-associated hypertrophy. Resident cardiac progenitor cells in ScaKI mice do not respond to pathological damage in vivo, consistent with observations of impaired growth and survival of ScaKI cardiac progenitor cells in vitro. The molecular basis of the defect in ScaKI cardiac progenitor cells is associated with increased canonical Wnt signaling pathway activation consistent with molecular characteristics of lineage commitment.'] Does sca-1 knockout impair myocardial and cardiac progenitor cell function?