The PMI (also known as the Point of Maximum Impulse) is the part of the body where the heart beat is felt the most. The PMI is felt best when you lie on the left side of your body, at approximately the 5th intercostal spaces (i.e. the spaces in between our ribs). On women, the left breast may need to be displaced upwards in order to find the 5th intercostal space. Simply count the spaces down from the clavicle until you reach the fifth gap. The diameter of the PMI is measured using finger pads. How many finger pads does it take to feel the whole span of the heart beat? Each finger pad corresponds to 1 centimeter (in metric units). A healthy PMI is 2.5 cm or less. An enlarged PMI may indicate cardiomegaly (i.e. heart enlargement).
Speaking of the heart, can you guess what this image means?
(I have this image printed on a T. shirt, by the way)