Normal fetal heart axis and position.

Cardiac position and axis were evaluated by ultrasound in 183 normal fetuses; both position and axis were found to be constant throughout gestational life. In the four-chamber view of the fetal heart, the normal axis lies at a 45 degree angle (range 22-75 degrees) to the left of an anteroposterior line drawn from the spine to the anterior chest wall. The normal position of the posterior portion of the heart can also be defined. The axis or position of the heart deviated from the established normal range in 15 cases, the outcome of which is discussed. Abnormal axis was associated with 50% mortality; abnormal position with 81% mortality. Deviation from the normal position of the fetal heart should initiate a search for an intrathoracic mass, whereas an abnormal axis is an indication for fetal echocardiography. Axis and position of the fetal heart are easily evaluated during a standard obstetric scan.