Table 1.

Some developmental events of the embryonic heart at various stages (S); post-ovulatory days (D)^*

S13 (28D) Heart with primitive ventricle and common atrium

S14 (43D) Pulmonary vein present: onset of aorticopulmonary septation

S15 (33D) Outflow tract cushions form in looping heart

S16 (37D) Semilunar valves begin forming in looped heart

S17 (41D) Ostium secundum and semilunar valves are formed; completion of aorticopulmonary septation

S18 (44D) Interventricular septum complete; septation of 4 chambers complete; appearance of septum secundum and foramen ovale

S19 (47D) Fusion of aortic and mitral endocardial cushion material; outflow tract septum formed and aortic and pulmonary streams divided

S20 (50D) Nerve processes and collagen appear in sinus node region

S21 (52D) Subepicardium becomes thicker

S22 (54D) Chordae tendinae begin forming

S23 (56D) SA and AV nodes evident; ganglion cells and immature neurons appear between aorta and pulmonary trunk; embryo’s length is double that of S18 Data from: McBride, et al., 1981; Orts-Llorca, et al, 1982; Leatherbury and Waldo, 1995; Conte and Pellegrini, 1984; Boucek, et al., 1984; Lomonico, et al., 1986; Wessels, et al., 2000; Magovern et al., 1986.

^*The approximate age for each stage is according to Olivier and Pineau, 1962.