Surface Anatomy of the Heart 
 
The heart, a muscular organ roughly the size of a clenched fist, lies obliquely within the mediastinum of the thoracic cavity. Its surface anatomy describes the external features visible on inspection or palpation of the heart’s outer surfaces.
 
Position and Orientation 
The heart lies between the lungs, posterior to the sternum, and rests on the diaphragm. Its long axis extends to the left fifth intercostal space near the midclavicular line, where the apex beat can be palpated. About two-thirds of the heart’s mass lies to the left of the midline. The organ is enclosed within the pericardium, and its external surfaces correspond to its internal chambers. 
 
Surfaces of the Heart 
The heart presents several distinct surfaces: anterior (sternocostal), inferior (diaphragmatic), left pulmonary, and right pulmonary. 
 
Anterior (Sternocostal) Surface: 
This surface faces anteriorly and is related to the sternum, costal cartilages, and anterior mediastinum. It is formed mainly by the right ventricle, with contributions from the right atrium and the left ventricle. The anterior interventricular (left anterior descending) groove runs vertically here, marking the boundary between the right and left ventricles. The right atrioventricular (coronary) groove separates the right atrium and ventricle and houses the right coronary artery. 
 
Inferior (Diaphragmatic) Surface: 
This surface rests on the central tendon of the diaphragm and is directed downward and backward. It is mainly formed by the left ventricle, with a smaller contribution from the right ventricle. The posterior interventricular (descending) groove runs along this surface, containing the posterior interventricular artery and the middle cardiac vein. The inferior surface is separated from the posterior surface by the coronary sinus, which runs transversely across its base. 
 
Left Pulmonary Surface: 
Formed primarily by the left ventricle and part of the left atrium, this surface lies in contact with the left lung. It appears smooth and rounded, corresponding to the cardiac impression on the medial aspect of the left lung. 
 
Right Pulmonary Surface: 
This surface is made up almost entirely of the right atrium, which receives the superior and inferior vena cava. It forms the right border of the cardiac silhouette on imaging. 
 
Borders of the Heart 
 
The heart has four borders: 
Right border: formed by the right atrium. 
Inferior border: mainly by the right ventricle, with a small part of the left ventricle. 
Left border: formed by the left ventricle and part of the left auricle. 
Superior border: formed by the right and left atria and the great vessels. 
 
Base and Apex 
 
The base of the heart faces posteriorly toward the vertebral column and consists mainly of the left atrium, with part of the right atrium. The apex, directed forward, downward, and to the left, is formed by the tip of the left ventricle and corresponds clinically to the apex beat at the fifth intercostal space. 
 
Clinical Relevance 
 
Knowledge of cardiac surface anatomy guides physical examination, interpretation of chest radiographs, and invasive procedures such as pericardiocentesis, where the pericardial sac is accessed near the left xiphisternal angle to avoid injury to the coronary vessels. 
 
Image provided by Servier Medical Art (https://smart.servier.com/), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).

Chest Radiograph with anatomical labels for reference: