Visualize the underlying structures of the heart as you inspect the anterior chest. Note that the right ventricle (RV) occupies most of the anterior cardiac surface. This chamber and the pulmonary artery form a wedgelike structure behind and to the left of the sternum, outlined in black (Fig. 1).

FIGURE 1. Chest wall and cardiac anatomy.

The inferior border of the RV lies below the junction of the sternum and the xiphoid process. The RV narrows superiorly and joins the pulmonary artery at the level of the sternal angle, or "base of the heart," a clinical term that refers to the superior aspect of the heart at the right and left 2nd interspaces adjacent to the sternum.

The left ventricle, behind the RV and to the left, forms the left lateral margin of the heart (Fig. 2). Its tapered inferior tip is often termed the cardiac apex. It is clinically important because it produces the apical impulse, identified during palpation of the precordium as the point of maximal impulse (PMI). This impulse locates the left border of the heart and is normally found in the 5th intercostal space at or just medial to the left midclavicular line (or 7 to 9 cm lateral to the midsternal line). The PMI is not always palpable, even in a healthy patient with a normal heart. Detection is affected by both the patient's body habitus and position during the examination.

FIGURE 2. Cardiac anatomy—major structures.

■ In supine patients the diameter of the PMI may be as large as a quarter, approximately 1 to 2.5 cm.

■ Note that, in some patients, the most prominent precordial impulse may not be at the apex of the left ventricle. For example, in patients with chronic obstructive pulmonary disease (COPD), the most prominent palpable impulse or PMI may be in the xiphoid or epigastric area due to right ventricular hypertrophy.

Above the heart lie the great vessels. The pulmonary artery bifurcates quickly into its left and right branches. The aorta curves upward from the left ventricle to the level of the sternal angle, where it arches posteriorly to the left and then downward. On the medial border, the superior and inferior venae cavae channel venous blood from the upper and lower portions of the body into the right atrium.

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