A fetal cardiac arrhythmia may cause misleading fetal heart rate tracings with unreliable signs of fetal distress. Assessment of such artifacts and of the hemodynamic relevance of a fetal arrhythmia by alternative methods is necessary for management and therapy. A 28-year-old healthy woman was referred at 30 weeks of gestation because of fetal tachy-brady-arrhythmia, but cw-Doppler assessment of umbilical artery blood flow revealed periods of pseudobradycardia during bigeminal and trigeminal fetal pulse. FHR turned to regular tachycardia, and transplacental digitalization was started. Between 32 and 34 weeks the patient discontinued her digitalis intake, and a fetal pericardial effusion indicated subsequent cardiac failure. Serial pulsed Doppler measurements of fetal aortic blood flow were performed and imminent heart failure was recognized after the digitalis was discontinued and before a pericardial effusion occurred. Furthermore, improvement of fetal cardiac performance secondary to restarting digitalis and also prior to resolution of the pericardial effusion. After spontaneous delivery a Wolff-Parkinson-White syndrome was diagnosed, and continuation of digoxin treatment was indicated. Cw-Doppler assessment of umbilical artery blood flow was a suitable method to evaluate questionable FHR recordings, and pulsed Doppler allowed monitoring of the therapeutic effect of transplacental digitalization by serial measurements of fetal aortic blood flow.