Cardiac arrhythmias and ECG abnormalities including bradycardia, prolongation of the QT interval, and atrioventricular (AV) conduction blocks have been extensively observed with fingolimod, the first marketed oral drug for treating the relapsing-remitting form of multiple sclerosis. This study was aiming to further elucidate the effects of fingolimod on cardiac electrophysiology at three different levels: (i) in vitro, (ii) ex vivo, and (iii) in vivo. (i) Patch-clamp experiments in whole cell configuration were performed on Ca 1.2-transfected tsA201 cells exposed to fingolimod-phosphate 100 or 500 nmol/L (n = 27 cells, total) to measure drug effect on L-type calcium current (I ). (ii) Langendorff perfusion experiments were undertaken on male Hartley guinea-pigs isolated hearts (n = 4) exposed to fingolimod 10 and 100 nmol/L to evaluate drug-induced effects on monophasic action potential duration measured at 90% repolarization (MAPD ). (iii) Implanted cardiac telemeters were used to record ECGs in guinea-pigs (n = 7) treated with a single dose of fingolimod 0.0625 mg/kg suspension, administered as an oral gavage. (i) In vitro cellular experiments showed that fingolimod-phosphate causes a concentration-dependent reduction in I . (ii) Ex vivo Langendorff experiments revealed that fingolimod had no significant effect on MAPD . (iii) Fingolimod caused significant prolongations of the RR, PR, QT, and QTc intervals in vivo. Reversible AV blocks were also observed in 7/7 animals. Fingolimod possesses I -blocking properties, further contributing to its AV conduction-slowing effects. These properties are also consistent with its mitigated effect on the QT interval in humans, despite previously shown HERG-blocking effect.