Third and fourth heart sounds also exist but are often difficult to hear using a stethoscope.

Heart Murmurs

Irregular sounds at rest may be indicative of valve malfunction. For example hissing sounds heard between the first and second heart sounds may indicate atrioventricular valve malfunction.

The most important examples of valve malfunction are:

1. Valve stenosis where the valve aperture is narrowed. This may arise from untreated streptococcal infections leading to rheumatic fever where the heart is inflamed, the heart rate increases and fever develops. This can lead to damage to the mitral valve and mitral stenosis. It may also be due to bacterial infection of the endocardium which may be due to the use of dirty needles by drug addicts.
2. Valve incompetence where valves become leaky and allow regurgitation of blood back into the atria. Again turbulence of blood flow may be heard as heart murmurs.