Several drugs have a QTc-prolonging effect and are metabolized by CYP3A4. The combination of QTc-prolonging drugs may act additive of the QTc interval. The risk increases additionally by co-administration of a CYP3A4-inhibiting substrate. This case report describes an incident with QTc prolongation which was probably caused by an interaction induced by a combination of amiodarone, clarithromycin and the CYP3A4-inhibitor fluconazole.