The Dimensions Of The Heart Are More Increased by the dilatation of its cavities than by hypertrophy. This dilatation (dilatatio cordis, also aneurysma cordis in the old writers), may, like hypertrophy, be total, affecting all the cavities of the heart, or partial, attacking only one of these portions. The excessive degree which dilatation may attain led the early anatomists to compare the human heart to that of a bullock.

Here also the most useful classification is that which is founded on the relation of the walls of the diseased portions of the heart.

1. Dilatation of the cavities of the heart may occur conjointly with hypertrophy of their walls, constituting aneurysma cordis activum (Cor-visart), and with eccentric hypertrophy.

2. Dilatation of the cavities of the heart may exist, associated with walls of normal thickness. This condition of simple dilatation - aneurysma cordis simplex - deserves equal attention with the above-named form of dilatation with hypertrophy, in as far as the normal thickness of the walls of the heart in dilatation of the cavities must necessarily depend on hypertrophy; it may therefore be regarded as an active dilatation - aneurysma cordis activum.

3. Dilatation of the cavities of the heart may occur in combination with attenuation and relaxation of the walls, constituting passive dilatation - aneurysma cordis passivum (Corvisart).

Besides these forms of dilatation, there are others connected with and dependent on alterations of texture, limited on one portion of a single cavity, and which we will pass over in the present case, reserving their consideration for a more suitable occasion, under the head of inflammations of the heart. We would here merely observe, that these forms of dilatation are known as partial dilatation and 'partial aneurism of the heart. As, however, we have applied the former of these terms to dilatation of a single division of the heart, and as, on the one hand, the term aneurism is unsuitable to the forms of dilatation under consideration, while, on the other, dilatation, combined with and dependent on alterations of texture, and such as attack only one portion of a cavity of the heart, exhibit great affinity with aneurisms of the arteries, we would designate these last named, which we pass over for the present, as true aneurism of the heart.

On considering the above-named forms of hypertrophy and dilatation, we find five, or perhaps more correctly speaking, four different conditions, and these will constitute the subject of the following remarks.

Simple Hypertrophy

Simple Hypertrophy, which is in general of rare occurrence, affects the ventricles, attacking the left one more frequently than the right. It probably continues to exist only for a certain period of indefinite duration, and then gradually merges into eccentric hypertrophy, that is to say, hypertrophy with dilatation. Although scarcely a doubt can be entertained of its existence, the attempt to confirm it is not devoid of difficulty.

The existence of concentric hypertrophy has been doubted by many who have made observations on the human subject after death, and prosecuted experiments on animals. In those who die from loss of blood, and occasionally after sudden and violent modes of death, the heart is indeed often in a condition of contraction, which might easily be mistaken for concentric hypertrophy. We cannot, however, agree with those who doubt the existence of concentric hypertrophy, which occurs, although rarely, in both ventricles, and, according to our observations, more frequently in the left. The cavity of this portion of the heart appears contracted in consequence of the thickening of the muscular wall, and of the papillary muscles, and the trabecule. Disease of the heart is manifested during life, and the symptoms exhibited correspond to the appearances observed after death.

Eccentric Hypertrophy

Eccentric Hypertrophy, active dilatation, including simple dilatation, is incomparably the most frequent condition. It attacks the ventricles as well as the auricles, and most frequently the cavities of the left side. Active dilatations originate in one portion of the heart, and, beginning at the left ventricle, gradually extend over the whole organ. This condition gives rise to the highest degrees of cardiac enlargement, which were known to the ancients under the terms enormitas cordis, cor tauri-num, etc. The enlargement is most strikingly manifested at the conus arteriosus of the right ventricle, whilst the space of the actual ventricle is generally contracted by the intrusion of the arch of the septum. The auricles are occasionally the special seat of active dilatation, and in these cases the disease commonly depends on contraction of the auriculo-ventricular opening on the same side. The wall of the auricle is stiff and rigid, and the cavity is not unfrequently filled with coagulated blood, or occasionally with stratified coagula of fibrin. These forms of dilatation have, however, been observed unassociated with this form of contraction.