The<unk>  (or obtuse<unk>  is shorter than the right border of heart, full, and rounded: it is formed mainly by the left ventricle, but to a slight extent, above, by the left atrium.
It extends from a point in the second left intercostal space, about 2.5 mm. from the sternal<unk> , obliquely downward, with a convexity to the left, to the apex of the heart.
Left margin of heart
Right border of heart
Diaphragmatic surface of heart
Sternocostal surface
Apex of the heart
Left sternal border
Sternal plane
Floating rib