It sometimes (though rarely) happens, that, with an increase of strength and bulk in its muscular structure, the left ventricle suffers a diminution of capacity in its cavity. In a case reported by Laënnec, the left ventricle was an inch and a half thick at its broadest, and an inch thick at its thinnest part; and yet its cavity was only capable of containing an unblanched almond. I have seen the same condition in a less degree.--(_Laënnec_, vol. ii. 698.) The circumstances under which these opposite conditions, this hypertrophy and atrophy of the heart, with the enlargement or diminution of its cavities, arise, must be explained hereafter. At present I would only remark that they are often found conjoined with actual disease in other structures of the heart, such as osseous or cartilaginous thickening of internal lining, adhesion of the pericardium, and ossification of the coronary arteries, to which they owe their origin; and, moreover, that they are often found where the heart is otherwise perfectly sound in texture, and where their cause must be sought in other parts of the body. The heart is liable to undergo a simple dilatation of its cavities without either thickening or attenuation of its muscular substance. This simple dilatation is sometimes of the whole organ, sometimes of one side, and sometimes only of one auricle or ventricle. When it is of one cavity only, it may be complicated with active or passive dilatation of another, or of all the rest. There is reason to believe that the heart sometimes undergoes a temporary dilatation, and again returns to its natural capacity; but that the dilatation can only subsist for a short time without becoming permanent. The power of thus enlarging its cavities, and restoring them to their natural condition, belongs more especially to the right side of the heart. A large accumulation of fat is sometimes met with about the heart. The healthy heart is always more or less marked upon its external surface with streaks of white, and this appearance results from the deposition of fat in the cellular texture, which unites the serous covering with the subjacent muscular structure. It is found principally where the venæ cavæ unite to form the right auricle; also at the base of the ventricles, and along the line which marks the boundary between the two, and around the origin of the great blood-vessels as they emerge from the heart. But when fat is deposited in more than these situations, and in more than the natural quantity, it is not so much added to the healthy substance of the heart, as existing at its expense and detriment, and the muscular structure is that which especially suffers. The fibre of the fat heart is pale and wasted, like that of a paralytic limb.--_Mus. of the Coll. of Surg._ 327.