An adrenergic receptor signaling pathway that contributes to a reduction in cardiac muscle contraction. Beta-adrenergic receptor-induced cardiac relaxation is achieved by a GPCR-activated adenylate cyclase generating cAMP; cAMP then activates the cAMP-dependent protein kinase A (PKA), which phosphorylates the sarcoplasmic reticulum (SR) membrane protein PLB. In its non-phosphorylated state, PLB acts as an inhibitor of the ATPase Ca(2+) pump of the cardiac SR (SERCA2a); inhibition of the pump is relieved upon phosphorylation. The pump removes Ca(2+) from the cytoplasm, thereby preventing cytosolic Ca(2+)-dependent activation of contractile proteins, leading to enhanced muscle relaxation.