Topography
The heart, wrapped in the pericardium, fills the middle mediastinum between the two lungs. It spans roughly the 3rd to 6th intercostal spaces and lies mostly left of the median plane. The base, where the great vessels leave, faces dorsocranially at mid-thoracic height; the apex points caudoventrally and to the left, close to the sternum and the costochondral junction of the 6th–7th rib.
Parts
- Right atrium and ventricle: receive blood from the venae cavae and pump it into the pulmonary trunk. The right ventricle forms the cranial border on a lateral radiograph.
- Left atrium and ventricle: the dorsocaudal left atrium receives the pulmonary veins; the thick-walled left ventricle forms the apex and ejects blood into the aorta.
- Valves: tricuspid (right atrioventricular), mitral (left atrioventricular), pulmonary and aortic.
Clinical relevance
- Auscultation: mitral area at the left 5th intercostal space at the costochondral junction; aortic area at the left 4th and pulmonic area at the left 3rd; tricuspid area at the right 3rd–4th intercostal space.
- Radiographic size: the vertebral heart score adds the long and short cardiac axes measured in thoracic vertebrae from T4; in most breeds the normal value is about 9.7 ± 0.5.
- Myxomatous mitral valve disease: the most common acquired heart disease, especially in small breeds.
- Dilated cardiomyopathy: typical of large and giant breeds (Dobermann, Great Dane).
- Patent ductus arteriosus: a common congenital defect, with a continuous murmur at the left heart base.
3D model
CT of a large-breed dog, registered onto the heart of the same abdominal study that provides the other organs and scaled to the skeleton. The great vessels were split off as pieces of their own (aorta, venae cavae, pulmonary trunk, pulmonary veins); this piece is the atria, auricles and ventricles.