The three vessel view (3VV) is an integral component of fetal cardiac screening. The evaluation of vessel size is subjective in this view.  Not infrequently, however, there can be a doubt and a need arises for objective assessment. Our aim was to clarify which ratio (AO/PA, AO/SVC, PA/SVC) can most easily judge the 3VV. We measured the diameter of the aorta (AO), pulmonary artery (PA) and superior vena cava (SVC) in 85 fetuses that had been diagnosed with a normal heart (NH) by the spatiotemporal image correlation (STIC) method and calculated the AO/PA ratio, AO/SVC ratio and PA/SVC ratio. We then calculated a similar index using an offline videotape in 15 fetuses diagnosed with coarctation of the aorta (COA), and 15 fetuses diagnosed with Tetralogy of Fallot (TOF). TOF excluded pulmonary atresia and absent pulmonary valve. All of the AO/PA ratios, AO/SVC ratios and PA/SVC ratios recognized a significant difference in the CoA, TOF and the NH groups. When we calculated the ROC curve in each CoA group and TOF group about AO/PA ratio, AO/SVC ratio, PA/SVC ratio, AO/PA ratio showed the highest sensitivity and specificity in the CoA group and the TOF group. When the cut-off value of the CoA for the NH group is AO/PA ratio < 0.7, good results are obtained, sensitivity is 100% and specificity is 90.6%. When the cut-off value of the TOF from the NH group is AO/PA ratio > 1.2, good results are obtained, sensitivity is 100% and specificity is 98.8%. The method to measure AO/PA ratio during heart screening can judge the 3VV objectively. When it exceeds 0.7 < AO/PA ratio < 1.2, it is likely to be congenital heart disease.