We compared the effects of ritodrine and atosiban treatments on fetal cardiovascular behavior by computerized nonstress test (c-NST) analysis. Women diagnosed with preterm labor were randomized to receive either atosiban or ritodrine. A c-NST was performed at least 12 hours after the last corticosteroid administration. Differences in fetal cardiovascular behavior were evident when treatment was given before 30 weeks' gestation. Ritodrine induced higher fetal heart rates, lower long-term variation values, and lower low:high-frequency ratios compared with atosiban. Atosiban induced higher gestational ages at delivery and higher birth weights than ritodrine. The mean Apgar scores were similar for atosiban and ritodrine groups at 1 and 5 minutes. No 5-minute Apgar score was < 7. With respect with atosiban, ritodrine treatment induces tachycardia and a lower variability of fetal heart rate. Such changes could be erroneously interpreted as signal of fetal distress, namely at lower gestational age.