Relaxin, a hormone of pregnancy, has shown broad cardioprotective effects including anti-fibrotic (reversed excess TGFβ signaling), anti-arrhythmic (Nav1.5 and INa upregulation and Cx43 phosphorylation and trafficking to intercalated disks) and anti-inflammatory properties (reduced IL-1β and IL-6). While relaxin’s anti-fibrotic effects are thought to occur through the SMAD2/3/TGFβ pathway, there is a general lack of understanding of relaxin’s mode of action to increase sodium current and alter connexin43 localization to suppress arrhythmias. Based on a rat model of aging, we tested the hypothesis that relaxin acts through activation of Wnt/β-catenin signaling to mediate its effects on Nav1.5 and Cx43 and to regulate collagen expression. We show for the first time that relaxin activates canonical Wnt signaling (increased nuclear β-catenin) to increase Nav1.5 in isolated cardiomyocytes. Block of canonical Wnt signaling (via Dikkopf-1) abrogated relaxin’s effect on both Nav1.5 in cardiomyocytes and suppression of excess collagen from fibroblasts. Further, we show that relaxin significantly suppressed expression of Dikkopf-1 in isolated cardiomyocytes and whole LV tissue. In addition, show that relaxin suppressed the age-associated genetic upregulation in inflammatory markers in a sex-dependent manner. Finally, we tested the hypothesis that relaxin would be an effective therapy in a rat model of pulmonary arterial hypertension and show that it reduced occlusion of small pulmonary arteries, myocardial and lung fibrosis and reversed the cardiac phenotype of ventricular arrhythmia or arrest. These results suggest that relaxin signals through multiple pathways to achieve its myriad effects and that relaxin has great potential as a therapy for multiple cardiopulmonary diseases
