The crisscross sign is a fetal ultrasound sign that describes the normal relationship between the ventricular outflows tracts of the fetal heart. The left ventricular outflow tract (LVOT); represented by the take-off of the aorta (Ao) from the left ventricle, is perpendicular (90o) to the right ventricular outflow tract (RVOT); represented by the take-off of the Pulmonary artery (PA) from the right ventricle. Hence, at the level of one ventricle outflow tract, its corresponding vessel (whether Ao or PA) would appear linear (straight/ tubular) while the other great vessel is circular.
If two tubular structures are seen coming out of the heart, one should think about the transposition of the great vessels.
NB: It should not be confused with the pathologic crisscross heart of atrio-ventricular discordance.
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