The cardiac impulse is the vibration resulting from the heart rotating, moving forward, and striking against the chest wall during systole.
Another theory for the occurrence of the PMI is the early systolic contraction of the longitudinal fibers of the left ventricle located on the endocardial surface of this chamber.
In children the apex beat occurs in the fourth rib interspace medial to the nipple.
Lateral and/or inferior displacement of the apex beat usually indicates enlargement of the heart, called cardiomegaly.
The character of the apex beat may provide vital diagnostic clues: Sustained apex beat, namely prolonged upward cardiac force during systole in a physical exam, can be seen in some chronic conditions such as hypertension and aortic stenosis, especially in elderly and females.