Original representative recordings of twitches (normalized to cross-sectional area) in non-failing human myocardium at basal status, in presence of Iso + Caff [isoproterenol (100 nmol/L)/caffeine (0.5 mmol/L)] and zacopride effective antiarrhythmic concentrations when arrhythmias in the form of extra systolic contractions with either high (A & B) or low (C & D) amplitudes are triggered in trabeculae isolated from both RV, right ventricle (heart # 415217 & 514489) and LV, left ventricle (heart # 219852 & 514489) of non-failing hearts, respectively. Original representative recordings of twitches (normalized to cross-sectional area) in failing human myocardium at basal status, in presence of Iso + Caff and zacopride effective antiarrhythmic concentrations when arrhythmias in the form of extra systolic contractions with either high (E & F) or low (G & H) amplitudes are triggered in trabeculae isolated from both RV (heart # 233587 & 645444) and LV (heart # 728878 & 645444) of failing hearts, respectively. IC50: median inhibitory concentrations of zacopride in the RV and LV of non-failing (I) and failing (J) human hearts.