It is possible that you mother has developed a very loud heart murmur. Murmurs are noises created by abnormal heart pathology. These can be related to defects in the valves or the walls of the heart, or other abnormalities. They can vary in volume from barely perceptible when a physician tries to listen with the stethoscope, to so loud that it can be heard even without a stethoscope. The fact that she experiences this when on her left side is probably due to the fact that the heart itself is located on the left, and when we lie on our left side, this increases the force of gravity on the blood returning to our heart, and can increase certain types of murmurs as a result.
In general, murmurs are a relatively stable phenomenon, especially if they are due to a defect in a valve or in a wall of the heart. It is possible, however, for a murmur to develop and/or become substantially louder in a short period, as you may be describing. This can involve acute failure of a valve, the acute development of an imperfection in the wall of the heart, or an acute increase in the volume of fluid that passes through an otherwise normal heart. Your mother may also be experiencing noise generated by an infection of the lining that surrounds the heart; if this is inflamed, it can rub against the heart muscle generating noise. Fluid can also collect between this lining and heart muscle, sometimes leading to noise as well.
Regardless of the possible etiology, you should have her examined promptly. If she has been experiencing any other symptoms (shortness of breath, chest pain, fainting/dizziness, etc.) as well, then this is even more concerning. In either case, have her examined as soon as possible either at the emergency room or by her physician (if he/she is available). This could be a benign condition, but it really should be worked up properly immediately.
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