Heart murmurs are most frequently organized by timing, into systolic heart murmurs and diastolic heart murmurs. However, continuous murmurs can not be directly placed into either category.^[1]

These murmurs are due to blood flow from a high pressure chamber or vessel to a lower pressure system.

• Patent ductus arteriosus . Patent ductus arteriosus (PDA) is an abnormal connection between the aorta and the pulmonary artery, which normally should be closed in infancy. Since aortic pressure is higher than pulmonary pressure, a continuous murmur occurs. This murmur is often described as a machinery murmur, or Gibson's murmur.^[2] This is named for George Alexander Gibson, who characterised it in 1898.^[3][4]
• Aortopulmonary window.
• Shunts. Usually a left to right shunt through a small atrial septal defect in the presence of mitral valve obstruction.