Figure 2 . Fetal echocardiography images from case 3 with Doppler and M-mode showing second-degree atrioventricular block with 2:1 AV conduction. (A) On initial consult for fetal right > left ventricular size discrepancy and probable coarctation of the aorta there was sinus rhythm at 138 bpm with mechanical PR=130 msec (B-D) On follow up, there was 2:1 AV conduction with regular atrial rates of 130-140 bpm and ventricular rates 65-70 bpm, as demonstrated by mitral inflow-aortic outflow Doppler [B], color M-mode [C], and hepatic vein Doppler [D], confirming regular atrial rates. (E) There was also a brief period of sinus bradycardia (92 bpm) with PR prolongation/first-degree AV block (mechanical PR interval 160-180 msec) (F-G) At next clinical follow ups, there was normal fetal heart rate and rhythm of 129-141bpm
(A)