Cardiac Murmurs





There are four heart sounds: 1st, 2nd, 3rd, 4th. The first two are caused by valves (closing the AV and the SL valves) and can easily be heard with a stethoscope.


The third and fourth heart sounds are caused by blood flow (by the rapid filling phase and the active filling phase) and are much softer and are often not heard.




Murmurs are abnormal sounds, in this case originating from the heart, and are often (but not always) caused by valve deficiencies.


There are two possible deficiencies: valvular stenosis (does not open properly) and valvular regurgitation (does not close properly). Valvular regurgitation is often also called: incompetence.


Depending upon the valve and the type of defect, a systolic or a diastolic murmur can occur.


For example; a mitral valve incompetence, will cause regurgitation when it should be closed, which is during cardiac systole and therefore will cause a systolic murmur.


A mitral stenosis on the other hand, which means it does not open properly, which should be the case during diastole, will then cause a diastolic murmur.



An aorta stenosis (does not open properly) will cause a murmur when blood flows through it, which is during the ejection phase, so during the ventricular contraction (= systole).


Note by the way the diamond shape of the murmur, which is caused by the initial increase followed by the subsequent decrease in the left ventricular pressure.


An aortic regurgitation occurs when the valves don’t close properly. This occurs of course during the diastole. This murmur indicates that blood is flowing back from the aorta into the left ventricle!


By the way, why are we only discussing the valves in the left heart and not those in the right heart?


In the computer labs in the NML, there is, in the computers, on the desktop, a folder labelled Learning Resources Material Index. Inside this folder, go to to the CVS table, which has two programs on Cardiac Sounds.


The first program (The physiological origins of heart sounds and murmurs) is pretty useful to walk through although maybe too detailed. Don’t forget to take your headphones with you or borrow one from the Circulation desk.


The second program (Beyond Heart Sounds) is probably too complicated and presents (only) cases, which are exhaustively discussed!