Fetal supraventricular tachycardia (FSVT) is characterized by an atrial frequency of 180 to 300 beats per minute (bpm) and a conduction rate of 1 : 1. The aim of this study is to establish the relationship between ejection fraction (EF) by planimetry in FSVT and cerebral blood flow through the Pulsatility Index (PI). Four patients with FSVT from the Maternal Fetal Medicine Unit HUS-UIS between January 2009 and March 2010. Clinical history, fetal anatomy, EF by planimetry with Simpson's method and fetal Doppler were performed. Treatment was established according to protocol. Equipment used: Medison 8000, statistical method based on Microsoft Excel 2007®. The maternal ages ranged between the 16 to the 35 years, the mean gestational age was 35.5 weeks, with related disorders such as hydrops fetalis, isoimmunization risk, gestational diabetes, maternal infection, and pericardial effusion. Reported Level II scan an average heart rate of 254.3 bpm and an average EF of 47.8%. The average fetal weight was 2503.6 g. The PI of the middle cerebral artery (MCA) average was 1.71 (P = 50). Sotalol treatment was maintained at a dose of 160 mg for an average of 5 days every 12 hours. Digoxin 0.1 mg was added twice a day and then once a day in two of the four cases, due to a non-response to Sotalol. Only one case required caesarean section for severe fetal bradycardia. None was taken to neonatal ICU. Planimetry shows no variation in relation to EF remaining above 30%, which is considered a normal value for the fetus. It suggests that low cardiac output due to high heart rate does not affect fetal hemodynamics in uterus. PI was found normal (P = 50). Diastole flow in MCA of was not found in any case suggesting a low flow in the brain in FSVT. 4. The highest the gestational age and fetal weight, the lowest the time the FSVT reverts.