The sounds of the heart afford to the physician a means of ascertaining with the utmost nicety the condition of the valves. If the sounds are altered from the normal in the least degree, the valves are not healthy. Alteration of the structure of a valve is in ordinary parlance heart-disease. It is usually indicated by an addition to the normal sound. Such addition is termed a “murmur”; in French, _un bruit de souffle_. Either term is somewhat misleading to the tyro. We remember a fellow-student to whom our chief had in vain expounded the nature of a murmur. “Surely, Mr. S., you can hear the murmur in this case.” We others could hear it as we stood around the bed. After listening for a minute, S. replied: “I think I could hear it, sir, if the heart wasn’t making such a thundering noise.” The thundering noise was the murmur. It is the business of the physician to recognize that there is a departure from the normal, to analyse its character, to determine the time at which it is heard in relation to the cardiac cycle, and to locate the place on the chest where it is heard most loudly. He is then in a position to state which of the valves is affected and what is the nature of its lesion. Is it a lesion obstructing an orifice, or is it causing regurgitation of blood? Or is one of the valves, as is commonly the case in heart-disease, imperfect in both respects? A murmur, in the strictest sense, is a sound added to a heart-sound. It is due in all cases to vibration of a fluid column (“fluid vein” is the term in physics). When fluid passing under pressure along a tube of a certain calibre enters a tube of smaller calibre, no vibration occurs. When it passes from a tube of smaller calibre into a larger tube or space, it is thrown into vibration. Under normal conditions no vibration occurs in the heart. The auriculo-ventricular orifices are so large that auricle and ventricle form a single cavity when the valve is open. The ventricles drive the blood into tubes of smaller dimensions than themselves. These are not the conditions which set up vibration in a fluid column. But if one of the orifices is constricted, owing to thickening or partial adhesion of its valve, the fluid column vibrates on entering the space beyond it. The sound is propagated forwards, beyond the constriction, not behind it, and transmitted to the wall of the ventricle, aorta, or pulmonary artery, as the case may be. When either of the auriculo-ventricular orifices is constricted, the vibration of the fluid column can be felt as well as heard. The finger placed against the chest-wall at the spot where the impulse of the heart occurs is sensible of a thrill. The vibration may occur whilst blood is flowing _through_ an auricle into a ventricle, before the auricle contracts. In time, it is presystolic. The murmur produced by regurgitation into an auricle is synchronous with systole. The murmur due to regurgitation into a ventricle past an incompetent semilunar valve is postsystolic.