BACKGROUND AND PURPOSE Hypoxia and subsequent re‐oxygenation are associated with cardiac arrhythmias such as early afterdepolarizations (EADs), which may be partly explained by perturbations in cytosolic calcium concentration. Transient receptor potential melastatin 4 (TRPM4), a calcium‐activated non‐selective cation channel, is functionally expressed in the heart. Based on its biophysical properties, it is likely to participate in EADs. Hence, modulators of TRPM4 activity may influence arrhythmias. The aim of this study was to investigate the possible anti‐arrhythmic effect of 9‐phenanthrol, a TRPM4 inhibitor in a murine heart model of hypoxia and re‐oxygenation‐induced EADs.EXPERIMENTAL APPROACH Mouse heart was removed, and the right ventricle was pinned in a superfusion chamber. After a period of normoxia, the preparation was superfused for 2 h with a hypoxic solution and then re‐oxygenated. Spontaneous electrical activity was investigated by intracellular microelectrode recordings.KEY RESULTS In normoxic conditions, the ventricle exhibited spontaneous action potentials. Application of the hypoxia and re‐oxygenation protocol unmasked hypoxia‐induced EADs, the occurrence of which increased under re‐oxygenation. The frequency of these EADs was reduced by superfusion with either flufenamic acid, a blocker of Ca²⁺‐dependent cation channels or with 9‐phenanthrol. Superfusion with 9‐phenanthrol (10⁻⁵ or 10⁻⁴ mol·L⁻¹) caused a dramatic dose‐dependent abolition of EADs.CONCLUSIONS AND IMPLICATIONS Hypoxia and re‐oxygenation‐induced EADs can be generated in the mouse heart model. 9‐Phenanthrol abolished EADs, which strongly suggests the involvement of TRPM4 in the generation of EAD. This identifies non‐selective cation channels inhibitors as new pharmacological candidates in the treatment of arrhythmias.