In spite of ongoing inotropic stimulation by ISO throughout the 3-week treatment time course, some strains displayed the same or decreased FS at later ISO time points compared to baseline, consistent with a decrease in contractile reserve—an observation in early HF stages of decreased cardiac function augmentation to direct inotropic stimulation—marked by reduced beta-adrenergic receptors along with altered sarcoplasmic reticulum Ca2+-adenosine triphosphatase 2a (SERCA2a) and phospholamban [54]. The gene discussed is PLN; the disease is hydrops fetalis.