Figure 1. Imaging the Xenopus tropicalis heart with OCT.

(a) Stage 46 tadpole embedded in 1% agarose and positioned so that the ventral side faces the OCT lens. Next, using a 5-axis stage, the embryo is oriented to the reference axis-mid eye plane. Finally, the heart is scanned from various angles to capture the three imaging planes. To capture the Ventral Three Chamber View (VTCV) and Outflow Tract View (OTV) we set the OCT imaging plane ± 0–15° to the reference axis and manually move the embryo posteriorly towards the tail on the y-axis until we capture the ventricle and the outflow tract. Similarly, to capture the Lateral View (LV) we adjusted the imaging plane ± 30–50° to the reference axis (b) Ventral Three Chamber View: Visualizes the single ventricle and both atria. Red dashed line marks the left atrium, right atrium, atrial septum, ventricle, atrioventricular valve, and trabecula in different stages of the cardiac cycle from systole to diastole (left to right). (c) Outflow Tract View: By moving the imaging plane anteriorly to the cranium, OCT captures the distal outflow tract including the spiral valve and systemic arteries. (d) Lateral View: Rotating the OCT beam angle 30–50 °C reveals the proximal outflow tract and the ventricle visualized during mid-systole. (e) Cardiac structures Resolved by OCT and Fate Mapping: Aortic arches; outflow tract, spiral valve and atrioventricular valve and ventricle; ventricle populated by primary and secondary heart field. (f) Xenopus tropicalis wildtype cardiac measurements by OCT and Histology. EDD: end diastolic diameter, ESD: end systolic diameter AV: atrioventricular, OFT: outflow tract, P: proximal, D: distal, StdD: standard deviation, SEM: Standard error of the mean, CoV: Coefficient of variation. Y-X Scale bar: 100 μm.