Final answer:
Normal heart sounds, such as the low-pitched, swishing sounds heard in the base of the lungs, are usually the S1 and S2 heart sounds, corresponding to the closing of the heart's valves. Abnormal heart sounds include murmurs and additional heart sounds like S3 and S4, which may indicate different cardiac or respiratory conditions.
Step-by-step explanation:
The normal, low-pitched, soft, swishing sounds heard throughout the chest and best heard in the base of the lungs during auscultation are indicative of normal blood flow through the heart's chambers and valves. These heart sounds, particularly S1 ("lub") and S2 ("dub"), are the sounds of the atrioventricular valves and semilunar valves closing during the cardiac cycle. Apart from these, a heart murmur and other abnormal sounds such as third and fourth heart sounds (S3 and S4) or a whooping sound associated with respiratory pertussis in infants can be indicative of certain medical conditions, which would need further evaluation.