The first sign of cardiac development is the cardiogenic plate that is still to be found cranially outside the embryo. The development of the heart then goes rapidly through 3 main phases:
- plexiform phase
- tubular phase
- loop phase
The flexion of the embryo causes the tissue of the original cardiogenic plate, which is enveloped by the pericardial cavity, to move into a ventral position. It consists of epicardium, myocardim and endocardium. A gelatinous mass, the cardiac jelly, temporarily forms between the myo- and endocardium and this is of decisive importance for the subsequent tube formation.
On the inside, diverse differentiation processes also take place whereby the blood is pumped through the heart, initially serially, and later in parallel. The following restructuring processes occur:
- Shifting of the inflow tract to the right
- Shifting the atrio-ventricular plane into the middle
- Dividing the atria and ventricles by septa
- Dividing of the outflow tracts by septa
The vessels near the heart are influenced in their development by the right-left determination of the heart. Certain portions of the venous and arterial systems atrophy and others develop further for this reason.
At birth large pressure changes take place. On the one hand, the low pressure area of the placenta falls away while, on the other hand, the pressure in the pulmonary circulation system decreases due to the distention of the lungs following the beginning of breathing. These two events cause the pressure in the left part of the heart to increase and in the right part of the heart to sink. The foramen ovale between the right and left atria closes thereby and the ductus arteriosus obliterates at the same time. Now the pulmonary circulation system is completely separated from the systemic one and they now operate in series.
The cardiac pacemaker and signal conduction system is important for a coordinated sequence of cardiac contractions. The sinus node is already delimited relatively early. The AV node and the bundle of His follow afterwards. Thanks to the sympathetic, parasympathetic and sensory innervation the heart can adequately deal with loads.
In cardiac pathologies cardiac vitia (defects) without shunts and those with shunts are distinguished. With the latter, there are right-left shunts that lead to a cyanosis as well as left-right shunts that are acyanotic. In addition, inlet abnormalities of the large vessels can be observed.