Ultrasound examination of a fetus at 32 weeks' gestation revealed dilated cardiomyopathy and a heart rate of 170 beats per minute. Prenatally, this mild tachycardia was not primarily suspected to be the cause of the myocardial changes. Postnatal electrocardiography revealed a persistent junctional reciprocating tachycardia (PJRT) and the diagnosis of tachycardia-induced cardiomyopathy (TICM) became apparent. After conversion to a sinus rhythm under digoxin and amiodarone, the cardiac changes regressed. PJRT is a rare form of supraventricular tachycardia. The prenatal findings in the condition have previously been described retrospectively, but it can only be diagnosed postnatally by its characteristic electrocardiographic properties. This case indicates that TICM can occur at lower heart rates than previously assumed. Even severe prenatal cardiomyopathy may be reversible once sinus rhythm has been restored.