A cone shaped, muscular, hollow organ that is situated between the two lungs on the left side of the chest. Its lower part lays in the middle of the tendinous diaphragm. The incoming and outgoing great vessels hold it in its place. It is divided into a widened upper part and a rounded off lower tip. Its size is generally the same as of a clenched fist, but there are differences according to age, gender, stature and the work of the heart. Looking at its surface we can see a furrow which divides it into two parts.

hearthThe two atria can be found at the top, the two ventricles at the bottom. There is an anterior and posterior furrow even between the ventricles which separate the ventricles. Coronary arteries, which supply the heart with nutrients, run in the furrows originated from the root of the main artery. The wall of the heart is made up of three layers. There is a shiny, double-walled serous membrane on the outer side that is called the pericardium. There is a small amount of serous fluid between the double laminae. Its central, and also its thickest part, is the cardiac muscle. It is a special striated muscle that functions in an involuntary manner and unites the positive qualities of the striated and smooth muscle. The ventricle wall is thicker, that of the atria is thinner, the former has three and the latter has two muscle layers. The strongest part of the heart is the left ventricle which performs the hardest work. The passage that leads from the atria to the ventricles, namely the atrioventricular gap, is surrounded by narrow rings made up of connective tissue separating the muscle of the atria and ventricles. The cusps of the atrioventricular valves are anchored to these rings. The inner layer of the heart is covered with endocardium which is thinner within the ventricles. The doubling of this covers the heart valves too. A longitudinal line divides its cell system into two separate, unconnected chambers, the right and the left heart chamber.

Taking the above-mentioned into consideration, the heart has four chambers. The atrias and ventricles are separated by heart valves. The right atrium and the right ventricle are separated by the tricuspid valve. Between the left atrium and left ventricle can be found the mitral valve. Great vessels enter into the heart through the atria then deliver the blood to the ventricle through the valves. Ventricles are the engines of blood circulation. Pulmonary circulation, together with the pulmonary artery, originates from the right ventricle, while the systemic circulation with the aorta from the left ventricle. The right part of the heart contains venous blood while the left part contains arterial blood.

Heart valves:
Allow blood to flow only in one direction.

  • atrioventricular valves: between the atria and ventricles
  • seminular valves: found in the root of arteries which leave the ventricles and in  the veins.

The rhythmical function of the heart is controlled by a separated impulse-leading and stimulus – generating system that is found within the heart, is made up of special muscle-fibres and it is in connection to the central nervous system.

The heart’s own impulse-leading and stimulus-generating parts:

  • sinoatrial node,
  • antrioventricular node,
  • antrioventricular bundle,
  • end branching.

The primary stimulus-generating place is the sinoatrial node which is the one that ensures the rhythm of cardiac contraction. The contraction of the heart is called the systole and its relax is called the diastole. The number of cardiac contractions is 60/80 per minute.