The heart has an important role in ensuring that the body tissues are continuously and well supplied with oxygen-rich blood and oxygen-poor blood extracted. The interventricular/Interatrial septum is important because it prevents oxygenated blood in the left side of the heart form mixing with deoxygenated blood in the right side of the heart.


The blood flows in two distinct circuits:

  • Pulmonary Circuit - in which deoxygenated blood is pumped from the right heart to the lungs. In the lungs the blood offloads Carbon dioxide and loads oxygen. This oxygenated blood is then pumped to the left side of heart from the lungs.


  • Systemic Circuit - in which oxygenated blood is pumped from the left side of heart to the body tissues. The blood offloads Oxygen as nutrient for the tissues and loads the waste product, Carbon dioxide. This deoxygenated blood then flows from the body tissues back to the right side of the heart. This flow of blood from the heart to the body tissues and back to the heart completes the circuit.


After the blood has passed through the systemic circuit and enters the heart via the Vena Cava, there is a series of contraction and relaxation of the heart. Due to this pressure changes, the closure of the heart valves during systole leads to 'lub-dub' sounds. There are three different heart sounds:

  • S1 - this is the first heart sound which is due to the closure of the Atrio-Ventricular valves. This sound is loud and long.
  • S2 - this is the second heart sound which is due to the closure of the Semi-lunar valves. This sound is softer and sharper.
  • S3 - this is a heart sound that can hardly be heard but is the result from the sudden filling of blood in the empty ventricles. This is during the Ventricular filling phase of the Cardiac Cycle. 

The heart sounds S1 and S2 are heard as the 'lub-dub'' sounds under the stethoscope.
Heart Murmurs are abnormal heart sounds which are usually associated with heart disease. If valves do not open fully this leads to turbulence blood flow which could be a reason for such murmurs. A Stenotic Valve ( abnormal narrowing opening of the valve) or an Insufficient Valve ( leaky valves allowing blood back flow) could result to mild murmurs. Rheumatic Fever is a common cause of heart murmurs.


The adult human heart pumps approximately 2,000 gallons of blood each day.