This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The heart becomes enlarged both by being dilated and by being hypertrophied, usually both conditions are present; and its position is often changed by disease both of itself and of adjacent organs. It is apt to enlarge unequally. In emphysema and bicuspid regurgitation the right side becomes enlarged, the pulmonary circulation being impeded. In aortic disease, arteriosclerosis, muscular exertion, or any cause impeding the course of the blood through the arteries there is produced an enlargement of the left side of the heart.
The average weight of the healthy heart is in the male 280 Gm. (9 oz.), and in the female 250 Gm. (8 oz.). These may be doubled in cases of enlargement. When the heart is enlarged the apex beat changes its position; it may occupy the sixth, seventh, or eighth interspace instead of the fifth, and may be as far as 5 to 7.5 cm. (2 to 3 in.) to the left of the nipple line.
When it enlarges upward, instead of the absolute dulness beginning opposite the fourth costal cartilage, it is opposite the third or even the second interspace. Toward the right side the absolute dulness may extend a couple of centimetres beyond the right edge of the sternum, instead of being near its left edge as is normal.
The heart is readily displaced by pressure from the surrounding structures. If there is abdominal distention by gas or ascites, or if the liver or spleen is enlarged, the heart is pushed upward. Enlargement of the liver may likewise depress the heart, if the patient is in an upright position, by the weight of the liver dragging it down. Aneurisms of the arch of the aorta, tumors, or emphysema may also depress it. In the aged the apex beat may be normally in the sixth interspace.
Lateral displacement occurs in cases of pleural effusion. Osier says ("Pract. of Med.," p. 594), this is not due to a twisting of the heart on its axis but to a positive lateral dislocation of the heart and pericardium. Pneumothorax or tumors on one side may also push the heart toward the opposite side. It may be pulled to one side by pleural adhesions and in those cases of fibroid phthisis in which the lung becomes markedly retracted. Abscess or tumors of the mediastinum also displace it.
The position of the pulsation of the heart is not always an indication of the position of the apex. In pleural effusion the pulsation may be one, two, or three interspaces higher than normal, while the apex itself may not be elevated.