**1. Introduction — Anatomy of the heart**

#### **1.1 Orientation of the heart within the thorax**

The mirror image of the heart to the anterior chest wall is a quadrilateral bounded by four angles: Upper left (the second intercostal space, 1 cm from the left sternal border), upper right (the second intercostal space, 1 cm from the right sternal border), lower left (the 5th intercostal space with the left midclavicular line corresponding to the apex of the heart), and lower right (the ascending space of the rib to the right border of the sternum).

In describing the orientation of a specific organ, such as the heart**,** the relationships are as follows:


**Figure 1.** *(a) Heart and lung (b) Cardiac anterior view (left) and posterior view (right).*

• Back of the heart: The posterior wall of the left atrium is directly related to the esophagus, so the cardiac image is clearly acquired through transesophageal echocardiography.
