The mammalian heart

Diagram of human heart

The four-chambered heart, along with the pulmonary and systemic circuits, completely separates oxygenated from deoxygenated blood. This allows for the higher metabolic rates needed by warm-blooded birds and mammals.

Parts not shown in diagrams:

  • Septum – separates the left and right ventricles
  • Coronary arteries >> read more here
  1. Branch out of aorta and wrap around the heart
  2. Transports oxygen and nutrients to atria (pl. of atrium), ventricles and septum

Diagram of heart with directions of blood flow

3D model of heart

Anatomy of a sheep’s heart


Parts of the heart and functions

Heart’s functions and how it works


How the heart pumps blood – cardiac cycle

Animation of how heart pumps blood >> from this website

The cardiac cycle consists of two parts:

  • systole (contraction of the heart muscle)
  • diastole(relaxation of the heart muscle).
  • Atria contract while ventricles relax.
  1. Deoxygenated blood flows from the body into the right atrium, through the superior and inferior vena cava.
  2. Blood flows from right atrium into right ventricle. (Atrium: systole, Ventricle: diastole) Valve: Tricuspid valve.
  3. Blood is pumped out of right ventricle to the lungs, through the pulmonary artery. (Ventricle: systole, Atrium: diastole) Valve: pulmonary (semi-lunar valve)
  4. Oxygenated blood flows from the lungs into the left atrium through pulmonary veins.
  5. Oxygenated blood flows into left ventricle. Valve: Mitral valve
  6. Oxygenated blood is pumped out of left ventricle to all parts of body through aorta. Valve: Aortic valve.
  7. Oxygenated blood is also transported to the atrium, ventricle and septum through coronary arteries.

Heart muscle contraction is due to the presence of nodal tissue in two regions of the heart.

  • The SA node (sinoatrial node) initiates heartbeat.
  • The AV node (atrioventricular node) causes ventricles to contract. The AV node is sometimes called the pacemaker since it keeps heartbeat regular.
  • Heartbeat is also controlled by nerve messages originating from the autonomic nervous system.



– under construction –


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