heart sounds

heart sounds With an ear applied to the chest — or more usually, with a stethoscope — it is normally possible to detect two sounds in every heart beat, which are produced when the valves of the heart close. The sounds arise from the brief turbulence of blood flow occurring just as a valve closes. The left side of the heart develops a higher pressure than the right side, which means that the sounds produced there, by the mitral (bicuspid) valve between atrium and ventricle, and the aortic valve at the exit from the ventricle, are generally louder and precede the sounds produced from the equivalent valves on the right side (tricuspid and pulmonary valves). The first heart sound is produced by closure of the two atrio–ventricular valves, when the ventricles start to contract. It is often described as ‘lub’; the ‘l’ reflecting the louder mitral valve closure preceding the quieter tricuspid valve closure ‘b’. Deep inspiration widens the split between mitral and tricuspid closure: ‘lu-ub’. The second heart sound is produced by closure of the aortic and pulmonary valves (between the ventricles and their respective arteries), and is often described as ‘dup’; the ‘d’ reflecting the louder aortic valve closure preceding the quieter tricuspid valve closure ‘p’. With experience, the two sounds can be distinguished by pitch and intensity; also at a resting heart rate there is a longer interval between beats than between the two sounds.

heart murmurs are soft sounds, like those made during a forcible expiration with the mouth open. They are most often caused by any departure from the crisp sounds described here which reflect equally crisp function of the valves. Valves may become leaky, allowing backflow (incompetence), or they may become stiff and narrow (stenosis). Stenosis, for example, of the aortic valve leads to an abnormal turbulence during ejection of blood through it from the left ventricle, so it is a systolic murmur because it occurs during the phase of contraction (systole), preceding the second heart sound at the closure of the valve. Incompetence of this same valve allows some blood to flow back into the ventricle causing a diastolic murmur at the time of the second sound when it closes incompletely during ventricular relaxation (diastole). An incompetent mitral valve allows blood to regurgitate into the left atrium throughout ventricular contraction, causing a systolic murmur, whereas mitral stenosis causes a murmur as the blood flows from atrium to ventricle during diastole.

Other characteristic murmurs are caused by congenital defects, such as a hole in the ventricular septum, or a failure of closure of the connection between aorta and pulmonary artery which is present before birth (patent ductus arteriosus).

A murmur is classified with respect to its intensity (just audible, soft, moderate, or loud), the point on the chest wall where the murmur is heard best (which assists its localization to a particular valve or part of the heart), and the timing of the murmur in the heart beat (in relation to the first and second heart sounds).

Not all murmurs signify abnormality of the heart. Systolic murmurs, due to normal turbulence during ventricular contraction and ejection of blood, may be present particularly in young people, and not uncommonly in exercise and in pregnancy.

David J. Miller, and Niall G. MacFarlane

See also heart; sounds of the body.