The heart develops from cardiac progenitor cells that migrate to the cardiogenic field and form blood islands that fuse to create the endothelial heart tube. The heart tube undergoes cardiac looping and septation to form the four-chambered heart. During septation, the atria, ventricles, and great arteries are partitioned. The aortic arches give rise to major blood vessels of the head and neck. By the end of the 7th week, septation is largely complete and the heart has transformed into a functional four-chambered pump.

1. By Dr Robin Thomas

2. By Dr Robin Thomas

3.  The vascular system appears in the middle of
3rd week , when embryo is no longer able to
satisfy its nutritional requirement .
 The Heart develops from splanchnopleuric
mesoderm related - intraembryonic coelom
that forms pericardial cavity. This mesoderm
called Cardiogenic area.

4. Cardiac development involves :
 1.Establishment of cardiogenic field
 2.Formation & position of heart tube
 3.Cardiac looping
 4.Cardiac septation

5.  Cardiac progenitor cells lie in the epiblast ,
lateral to primitive streak.
 Migrate towards primitive streak
 Cells destined to form cranial segments of heart ,
outflow tract, migrate first & cells forming more
caudal portions , right ventricle,
left ventricle & sinus venosus migrate in
sequential order.
 Cells procede towards cranium & position
themselves rostral to buccopharyngeal
membrane & neural folds- reside in splanchnic
layer of lateral plate mesoderm.

6.  Cardiac progenitor cells lies – epiblast ,lateral
to primitive streak. Cells procede towards
cranium –rostral to buccopharyngeal
membrane & neural folds. Reside in
splanchnic layer of lateral plate mesoderm.

7.  Blood islands appear in this mesoderm –form
bloodcells & vessels –vasculogenesis.
 Blood islands unite & form horseshoe shaped
endothelial lined tube surrounded by
myoblasts- cardiogenic field – intraembryonic
cavity over it develops into pericardial cavity.

8.  Initially central portion of cardiogenic area is
anterior to buccopharyngeal membrane & neural
plate.
 Closure of neural tube & formation of brain
vesicles – central nervous system grows cephalad
 Buccopharyngeal membrane is pulled forward –
heart & pericardial cavity move first to cervical
region & finally to thorax.
 Embryo fold cephalocaudally & laterally- caudal
region of paired cardiac primordia merge.

9.  18 Days embryo 20 Days embryo
 Central portion- cardiogenic area anterior to
buccopharyngeal membrane & neural plate.

10.  21Days embryo 22 Days embryo
growth of brain & buccopharyngeal memb
cephalic folding of pulled forward –heart &
embryo. pericardial cavity moves
first to cervical region-
thorax.

11.  22 day embryo
 Embryo folds cephalocaudally & laterally-caudal
region of paired cardiac primordia merge-
 Heart –continuous expanded tube with inner
endothelial lining & outer myocardial layer. Pump
blood –first aortic arch –dorsal aorta.

12.  Heart - continuous expanded tube – inner
endothelial lining & outer myocardial layer.
 Receives venous drainage at caudal pole - pump
blood - first aortic arch into dorsal aorta .
 Heart tube - attached to pericardial cavity by
dorsal mesocardium.
 Dorsal mesocardium disappears-creates
transverse pericardial sinus-connects both sides
of pericardial cavity.
 Myocardium thickens & secrete thick layer of
extracellular matrix – rich in hyaluronic acid –
separates from endothelium.

13.  Mesothelial cells on surface of septum
transversum form proepicardium-later form
epicardium.
 Heart tube consists of 3 layers
Endocardium-internal endothelial lining
Myocardium-muscular wall
Epicardium-outside of heart tube

14.  Right & left endothelial
heart tubes.
 Fusion of heart tubes
from cranial to caudal
ends.

16.  Arterial end of heart tube Venous end of
heart tube

17.  Single endothelial heart tube shows series of
dilatations.
 1.Bulbus cordis
 2.ventricle
 3.atrium
 4.sinus venosus

18.  Ventricle & atrium are connected by
atrioventricular canal.
 Sinus venosus has prolongations - right & left
horns.
 Bulbus cordis lies at arterial end of heart tube
–divisible into proximal part - conus &
distal part - truncus arteriosus.
 Truncus arteriosus continuous distally with
aortic sac-continuous with right & left
pharyngeal arch arteries-continuous with
right & left dorsal aorta.

19.  Sinus venosus lies at venous end of heart-has
right & left horns.
 One vitelline vein (yolk sac), umbilical vein
(placenta), common cardinal vein (bodywall)
join each horn of sinus venosus.

20.  Heart tube elongate & bend on day 21.
 Cephalic portion bend ventrally,caudally & to
right.
 Atrial portion shift dorsocranially & to left.
 Bending creates cardiac loop-complete by
day 28.

21.  Cephalic portion heart tube bend ventrally,
caudally & to right.
 Atrial portion shift dorso-cranially & to left.
Creates Cardiac loop-complete by day 28.

23.  Dextrocardia-heart loops to left instead of
right.
 Heart lies on right side of thorax instead of
left.
 May coincide with situs inversus-complete
reversal of asymmetry in all organs.

25.  Truncus arteriosus form ascending aorta &
pulmonary trunk.
 Conus absorbed into ventricle & form
chamber –partitioned into right & left
ventricles.
 Primitive atrium partitioned into right & left
atria.
 Sinus venosus absorbed into right atrium.
 Right common cardinal vein forms superior
vena cava.

26.  Umbilical vein disappears.
 Right vitelline vein forms part of inferior vena
cava.
 Left horn of sinus venosus retrogresses-form
part of coronary sinus.

29.  Sinus venosus & primitive atrial chamber are
connected by a wide opening
 Opening becomes narrow-shifts to right-
narrow slit-right & left venous valves.
 Cranially 2 valves fuse to form septum
spurium.
 Atrioventricular canal divides into right & left
halves.
 2 thickenings-atrioventricular cushions
appear on dorsal & ventral walls.

30.  Atrio ventricular cushions grow towards each
other & fuse –form septum intermedium.

32.  Begins at day 26-ingrowth of large tissue
masses.
 Endocardial cushions at atrio ventricular &
conotruncal junctions.
 Endocardial cells de differentiate & form part of
atrio- ventricular valves.
 Complete septation of atrioventricular canal –
fusion of endocardial cushions.
 Most of atrioventricular valve tissue –derived
from ventricular myocardium –undermining of
ventricular walls.

33.  Physical separation of 2 valves (mitral &
tricuspid valve) produce atrioventricular
septum.
 Absence causes-Atrio ventricular canal
defects. (Endocardial cushion defects)

34.  1.Complete endocardial cushion defects
Ostium primum ASD, VSD in interventricular
septum, clefts in anterior mitral valve & septal
leaflet of tricuspid valve.
 2.Partial endocardial cushion defects
Ostium primum ASD, clefts in mitral &
tricuspid valve.

39.  Septation of atria begins at day 30 day .
 Atrial chamber undergoes division into right
& left halves-formation of 2 septa.
 Septum primum arises from roof of atrium ,
to right of septum spurium.
 Septum primum grows downwards & fuses
with atrioventricular cushions.
 Upper part of septum primum degenerates-
form foramen secundum.

40.  Septum secundum formed to right of septum
primum.
 Septum secundum grows downwards from
roof of atrial chamber-overlapps free edge of
septum primum.
 Blood now flows from left to right through
oblique cleft b/w 2 septa-foramen ovale.
 During fetal life oxygenated blood reaches
right atrium from placenta.
 Blood reaches left atrium tru foramen ovale.

41.  After birth left atrium receives oxygenated
blood from lungs- foramen ovale obliterated
by fusion of septum primum & septum
secundum.
 Annulus ovalis –septum secundum.
 Fossa ovalis-septum primum.

42. Inter atrial septal defects
 1.Septum primum defect
 2.Septum secundum defect
 3.Patent foramen ovale
 4.Premature closure of foramen ovale

44.  Right atrium derived from :
1.Right half of primitive atrium-main part.
2.Sinus venosus.
3.Right half of Atrio ventricular canal.

45.  SINUS VENOSUS
 Left horn of sinus venosus –part of coronary
sinus.
 Right common cardinal vein becomes part of
superior vena cava.
 Right vitelline vein forms terminal part of
inferior vena cava.
 Right venous valve (right margin of sinu atrial
orifice) forms crista terminalis, valve of IVC,
& valve of coronary sinus.

47.  Left atrium is derived from :
1.Primitive atrial chamber-left half
2.Atrioventricular canal-left half
3.Pulmonary veins -absorbed proximal parts
 Single pulmonary vein opens into left half of
atrium –when septum primum just beginning to
form.
 Pulmonary vein bifurcates-right & left branches-
bifurcates-drain corresp. lung bud.
 Parts of pulmonary vein nearest to left atrium –
absorbed -4 pulmonary veins

49.  Fate of Bulbus Cordis
 Bulbus Cordis –divisible into conus (proximal
part) & truncus arteriosus (distal part).
 Spiral septum –union of right superior & left
inferior truncus swelling or cushions.
 Spiral septum appears within truncus
arteriosus & subdivides into ascending aorta
& pulmonary trunk.

50.  Conus (bulbus cordis proper) merges with
cavity of primitive ventricle .
 Right & left ventricle formed –partition of this
chamber.
 Bulboventricular cavity consists of :
Dilated lower part –communicates with atria.
Conical upper part-communicates with
truncus arteriosus.

54.  Septation of ventricles begins at day 25.
 Interventricular septum grows upwards from
floor of bulboventricular cavity-divides lower
dilated part into right & left halves.
 Interventricular septum fuses with fused
atrioventricular cushions.
 Right & left bulbar ridges arise from conical part
of bulboventricular cavity & fuse to form bulbar
septum.

55.  Bulbar septum grows towards interventricular
septum , doesnot reach it –gap left b/w two.
 Gap b/w upper edge of interventricular
septum & lower edge of bulbar septum –filled
by proliferation of tissue from atrioventricular
cushions.

56.  Inter ventricular septal defects
 1.VSD
 2.Tetralogy of Fallot
 3.Persistant truncus arteriosus
 4.Transposition of Great arteries

61.  Mitral & tricuspid valves formed –proliferation
of connective tissue under endocardium of
right & left atrioventricular canals.
 Pulmonary & aortic valves –endocardial
cushions formed at junction of truncus -
arteriosus & conus.

63.  3rd week of life ( 15-21 days)
 1.Splanchnopleuric mesoderm-18 days.
 2.Cavitation of mesoderm-intraembryonic
coelom-pericardial, pleural, peritoneal
cavities-18 days.
 3.Endocardial heart tube-20 days.
 4.Cardiac looping-21days.

64.  4 th week of life ( 22-28 days )
 1.Dvp. of left ventricle & right ventricle.
 2.Circulation commences.
 3.Cardiovascular septation.
 4.Aortic arches begins.

65.  5 th week of life ( 29-35 days )
 1.LV,RV,ventricular septum continue to grow.
 2.Approximation of aorta to interventricular
foramen, mitral valve,LV.
 3.Separation of ascending aorta,main
pulmonary artery.
 4.Separation of mitral & tricuspid valve.
 5.Tricuspid valve opens into right ventricle.
 6.Ostium primum closed by endocardial
cushions.

66.  6th & 7th week of life ( 36-49 days )
 1.Closure of conal septum
 2.Closure of membraneous part of ventricular
septum 38-45 days

67.  Blood vessel development by 2 mechanisms.
 1.Vasculogenesis-vessels arise by coalesence
of angioblasts.
 2.Angiogenesis-vessels sprout from existing
vessels.
 Dorsal aorta & cardinal veins –vasculogenesis.
 VEGF-vascular endothelial growth factor.

73.  Pharyngeal arches develop during 4 th & 5th
weeks of development.
 First arteries to appear in embryo-right & left
primitive aortae.
 Continuous with 2 endocardial heart tubes.
 Each primitive aorta-ventral aorta (lying
ventral to foregut), arched portion & dorsal
aorta (lying dorsal to gut).

74.  Fusion of 2 endocardial heart tubes-2 ventral
aorta partially fuse to form aortic sac.
 Unfused parts remain as right & left horns of
sac.
 Successive arterial arches appear in 2-6
pharyngeal arches, each connected ventrally
to right or left horn of aortic sac & dorsally to
dorsal aorta.

75.  Greater part of 1st & 2nd arch arteries
disappear ( 29 day embryo )
 Small portion of 1st arch artery persists to
form maxillary artery.
 Second arch artery form hyoid & stapedial
artery.
 Fifth arch artery also disappears.
 Aortic sac now connected with arteries of 3,4
& 6th arches.


76.  3rd & 4th arteries open into ventral part & 6th
arch arteries into dorsal part of aortic sac.
 Spiral septum formed in truncus arteriosus
,extends into aortic sac –fuses with posterior
wall-blood from pulmonary trunk passes into
6th arch artery –blood from ascending aorta
passes into 3rd & 4th arch arteries.
 Dorsal aorta b/w 3rd & 4th arches disappear
on both sides.

77.  Each 6th arch artery gives off artery to
developing lung bud.
 Right side-portion of 6th arch artery b/w lung
bud & dorsal aorta disappears.
 Left side-remains patent & forms ductus
arteriosus.
 Each 3rd arch artery gives off a bud –grows
cranially & form external carotid artery.

78.  Dorsal aorta gives off series of lateral
intersegmental branches to body wall.
 7th cervical intersegmental artery forms left
subclavian artery.

79. Arch Arterial derivative
1 arch Maxillary artery
2 arch Hyoid & stapedial artery
3 arch Common carotid & 1st
part of internal carotid
artery.
Left side of 4th arch Arch of aorta ( from left
common carotid to left
subclavian arteries ).
Right side of 4th arch Right subclavian artery
(proximal portion)
Left side of 6th arch Left pulmonary artery &
ductus arteriosus
Right side of 6th arch Right pulmonary artery

80.  Ascending aorta & pulmonary trunk –formed
from truncus arteriosus.
 Arch of aorta –from aortic sac, its left horn,
left 4th arch artery.
 Descending aorta-from left dorsal aorta,
partly from fused medial vessel.
 Brachiocephalic artery from right horn of
aortic sac.
 Common carotid artery from part of 3rd arch
artery.

81.  Pulmonary artery from 6th arch artery.
 Arteries to the gut-from ventral splanchnic
branches of dorsal aorta.
 Renal,supra renal & gonadal arteries –from
lateral splanchnic branches of dorsal aorta.
 Left subclavian artery –part of 7th cervical
intersegmental artery. Right side partly from
7th cervical intersegmental artery & right 4th
arch artery.

82.  Portal vein from right & left vitelline veins &
anastomosis b/w them.
 Superior vena cava from part of right anterior
cardinal vein & right common cardinal vein.
 Inferior vena cava from right posterior
cardinal vein, right subcardinal vein, right
supra cardinal vein, right hepato cardiac
channel.

83.  Heart develops from splanchnopleuric
mesoderm-cardiogenic area-3rd week.
 1.Establishment of cardiogenic field
2.Formation & position of heart tube
3.Cardiac looping
4.Cardiac septation
5.Aortic arch dvp.
 Heart begins to beat by day 22.

84.  Cardiogenesis begins on 18th day of life &
normally completed by 45th day of life with
formation of membraneous part of
interventricular septum.

85.  1.Kliegman, Stanton, Geme ST, Schor, Behrman. Nelson
Textbook of Pediatrics 19th edition 2012 :1527-1529.
 2.Sadler WT. Langmans Medical Embryology 10th edition
2012 :159-189.
 3.John FK, James EL, Donald CF Nadas Pediatric
Cardiology 2nd edition :14-25
 4.Myung K Park .Pediatric cardiology for Practitioners 2012
5th edition 120-180
 5.Inderbir singh, Pal PK. Human Embryology 8th edition
2012 :191-231