Cardiovascular disease-related deaths frequently arise from arrhythmias, but treatment options are limited due to perilous side effects of commonly used antiarrhythmic drugs. Cardiac rhythmicity strongly depends on cardiomyocyte Ca(2+) handling and prevalent cardiac diseases are causally associated with perturbations in intracellular Ca(2+) handling. Therefore, intracellular Ca(2+) transporters are lead candidate structures for novel and safer antiarrhythmic therapies. Mitochondria and mitochondrial Ca(2+) transport proteins are important regulators of cardiac Ca(2+) handling. Here we evaluated the potential of pharmacological activation of mitochondrial Ca(2+) uptake for the treatment of cardiac arrhythmia. To this aim,we tested substances that enhance mitochondrial Ca(2+) uptake for their ability to suppress arrhythmia in a murine model for ryanodine receptor 2 (RyR2)-mediated catecholaminergic polymorphic ventricular tachycardia (CPVT) in vitro and in vivo and in induced pluripotent stem cell-derived cardiomyocytes from a CPVT patient. In freshly isolated cardiomyocytes of RyR2(R4496C/WT) mice efsevin, a synthetic agonist of the voltage-dependent anion channel 2 (VDAC2) in the outer mitochondrial membrane, prevented the formation of diastolic Ca(2+) waves and spontaneous action potentials. The antiarrhythmic effect of efsevin was abolished by blockade of the mitochondrial Ca(2+) uniporter (MCU), but could be reproduced using the natural MCU activator kaempferol. Both mitochondrial Ca(2+) uptake enhancers (MiCUps), efsevin and kaempferol, significantly reduced episodes of stress-induced ventricular tachycardia in RyR2(R4496C/WT) mice in vivo and abolished diastolic, arrhythmogenic Ca(2+) events in human iPSC-derived cardiomyocytes.