In horses, twin pregnancy is pathological and represents a potentially life-threatening condition to the mare and foal. Twinning occurs in approximately 2% of pregnancies. Of these, the majority of cases are dizygotic twins, resulting from 2 ovulations and monozygotic twins are rare. A 12-year-old Quarter Horse mare was presented for breeding management with shipped cooled semen and embryo transfer. Seven days post ovulation, a single late morula/early blastocyst was recovered and transferred immediately to a recipient mare. Thirty-six days after transfer, transrectal ultrasound examination revealed the presence of 2 embryos. A transcutaneous reduction of one of the fetuses was performed successfully at 128 days of gestation. This report is the first to describe a successful reduction of monozygotic twins by transcutaneous ultrasound-guided cardiac puncture.