Background: Relax-Cardio is a multicenter, randomized, double-blind, crossover placebo-controlled Phase II study to assess the effect of serelaxin versus placebo on high-sensitivity cardiac troponin I (hs-cTnI) release in patients with chronic heart failure after exercise when used in addition to standard of care. Trial Registration No: NCT02625922 (clinicaltrials.gov) Link Trial Status: Randomized worldwide: 16 (of N=120) Randomized in Basel: 3 (of N=10) Enrolling Centers: Switzerland Worldwide: University Hospital Basel 4 in Germany 4 in UK Core Study Team: