BACKGROUND AND PURPOSE:Expression of the pro-fibrotic galectin-3 and the pro-apoptotic BIM is elevated in diseased heart or after β-adrenoceptor stimulation, but the underlying mechanisms are unclear. This question was addressed in the present study. EXPERIMENTAL APPROACH:Wild-type mice and mice with cardiac transgenic expression of β2 -adrenoceptors, mammalian sterile-20 like kinase 1 (Mst1) or dominant-negative Mst1, and non-specific galectin-3 knockout mice were used. Effects of the β-adrenoceptor agonist isoprenaline or β-adrenoceptor antagonists were studied. Rat cardiomyoblasts (H9c2) were used for mechanistic exploration. Biochemical assays were performed. KEY RESULTS:Isoprenaline treatment up-regulated expression of galectin-3 and BIM, and this was inhibited by non-selective or selective β-adrenoceptor antagonists (by 60-70%). Cardiac expression of galectin-3 and BIM was increased in β2 -adrenoceptor transgenic mice. Isoprenaline-induced up-regulation of galectin-3 and BIM was attenuated by Mst1 inactivation, but isoprenaline-induced galectin-3 expression was exaggerated by transgenic Mst1 activation. Pharmacological or genetic activation of β-adrenoceptors induced Mst1 expression and yes-associated protein (YAP) phosphorylation. YAP hyper-phosphorylation was also evident in Mst1 transgenic hearts with up-regulated expression of galectin-3 (40-fold) and BIM as well as up-regulation of many YAP-target genes by RNA sequencing. In H9c2 cells, isoprenaline induced YAP phosphorylation and expression of galectin-3 and BIM, effects simulated by forskolin but abolished by PKA inhibitors, and YAP knockdown induced expression of galectin-3 and BIM. CONCLUSIONS AND IMPLICATIONS:Stimulation of cardiac β-adrenoceptors activated the Mst1/Hippo pathway leading to YAP hyper-phosphorylation with enhanced expression of galectin-3 and BIM. This signalling pathway would have therapeutic potential. LINKED ARTICLES:This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.