Phospholamban phosphorylation at the serine 16 residue in pediatric (A and B) and adult (C and D) myocardium; representative Western blot and quantitation for each are shown. GAPDH was used as a loading control. Ser16, serine 16 residue; pPLB, phospholamban phosphorylation; PLB, phospholamban; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; NF, non-failing; F, failing; FT, failing treated with PDE3i.