The mammalian heart is composed of mainly two cell types that are responsible for proper organ function. Cardiac myocytes (shown in green) constitute the muscle portion of the heart and execute the ‘beating’ functions necessary for pumping blood. These cells largely stay the same from the time of birth. In contrast, cardiac fibroblasts, shown here in red, are readily replenishable and aid in cardiac function by secreting extracellular factors and signaling molecules. Field width 0.21 mm. Image by Efrain Rivera Serrano. Research group: Dr. Barbara Sherry, Molecular Biomedical Sciences.