In a cascade mediated by a GPCR known as β adrenoceptor, activated by catecholamines (notably norepinephrine), PKA gets activated and phosphorylates numerous targets, namely: L-type calcium channels, phospholamban, troponin I, myosin binding protein C, and potassium channels. This increases inotropy as well as lusitropy, increasing contraction force as well as enabling the muscles to relax faster.