Restoration of a positive inotropic response of hES2-ventricular cardiomyocytes (vCMs) by phospholamban (PLB) overexpression. A, Representative raw tracings of electrically induced Ca2+ transients of untransduced, adenovirus (Ad)-green fluorescence protein (GFP)–transduced, Ad-PLB–transduced, and Ad-S16E-PLB–transduced human embryonic stem cell (hESC)–derived vCMs paced at 1 Hz recorded in the absence and presence of isoproterenol (Iso) as indicated. Peaks recorded under control drug–free condition of all groups have been normalized for comparison. B, Bar graphs summarizing the transient parameters of the same groups from (A). Ad-PLB–transduced hESC-vCMs uniquely responded to Iso (n=15, 15, 15, and 25 for control, Ad-GFP, Ad-PLB, and Ad-S16E-PLB respectively; **P<0.01, compared with parameters under drug-free condition).