BACKGROUND AND PURPOSEAtrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with an increased risk for stroke, heart failure and cardiovascular-related mortality. Candidate targets for anti-AF drugs include a potassium channel Kv1.5, and the ionic currents IKACh and late INa, along with increased oxidative stress and activation of NFAT-mediated gene transcription. As pharmacological management of AF is currently suboptimal, we have designed and characterized a multifunctional small molecule, compound 1 (C1), to target these ion channels and pathways. EXPERIMENTAL APPROACHWe made whole-cell patch-clamp recordings of recombinant ion channels, human atrial IKur, rat atrial IKACh, cellular recordings of contractility and calcium transient measurements in tsA201 cells, human atrial samples and rat myocytes. We also used a model of inducible AF in dogs. KEY RESULTSC1 inhibited human peak and late Kv1.5 currents, frequency-dependently, with IC50 of 0.36 and 0.11 μmol·L −1 respectively. C1 inhibited IKACh (IC50 of 1.9 μmol·L −1 ) and the Nav1.5 sodium channel current (IC50s of 3 and 1 μmol·L −1 for peak and late components respectively). C1 (1 μmol·L −1 ) significantly delayed contractile and calcium dysfunction in rat ventricular myocytes treated with 3 nmol·L −1 sea anemone toxin (ATX-II). C1 weakly inhibited the hERG channel and maintained antioxidant and NFAT-inhibitory properties comparable to the parent molecule, resveratrol. In a model of inducible AF in conscious dogs, C1 (1 mg·kg −1 ) reduced the average and total AF duration. CONCLUSION AND IMPLICATIONSC1 behaved as a promising multifunctional small molecule targeting a number of key pathways involved in AF. AbbreviationsAERP, atrial effective refractory period; AF, atrial fibrillation; BCL, basic cycle length; CABG, coronary artery bypass graft surgery; C1, compound 1; DPPH, diphenylpicrylhydrazyl; NRVM, neonatal rat ventricular myocytes BJP British Journal of Pharmacology