This condition is one of comparatively frequent occurrence, but is for the most part merely a part of general atrophy, or emaciation of the body. In emaciating diseases where the muscular system as a whole has undergone great reduction in bulk, the heart is found to take part in the same process. Taking the normal weight of the heart as 9 ounces for the female, and 10 or 11 ounces for the male, we may find it reduced to 6 or even 5 ounces. Viewed as a whole the heart is obviously smaller, and it has a darker colour than normal, while the coronary arteries stand out unduly, often as somewhat prominent tubes. This change of colour and the prominence of the arteries are largely due to the loss of the sub-pericardial fat, which normally covers the greater part of the surface and accompanies the coronary arteries, partially embedding them in the adipose tissue.

The muscular substance when incised is found to be deeper in colour and tougher than usual. On account of this the name of Brown atrophy is given. With the atrophy of the muscular fibres there is a concentration of pigment granules around the nuclei. In nearly all old persons there is at the two poles of each nucleus a group of brown pigment granules, and these increase greatly. There is also frequently a distinct demarcation of the cells which constitute the muscular cylinders, an appearance which is not normally present. This has, without sufficient grounds, been interpreted as an indication of disintegration of the muscle. Brown atrophy may be associated with fatty degeneration, the brown pigment being distinguishable by its colour from the fat granules.