The "acute margin" refers to the anteroinferior border of the heart. It is also known by its Latin name [margo acutus].
The name of this border or margin of the heart is quite descriptive. If you observe the angle formed between the anterior or sternocostal surface of the heart with the posterior or diaphragmatic surface of the heart, you can see that the angle between these two surfaces is less than 90 degrees, therefore an "acute" angle. The corresponding border between these two surfaces has to be called the "acute margin"!
In relation to the acute margin of the heart there is usually found one of the longest branches of the right coronary artery. This artery that runs alongside the acute margin, is the "acute marginal artery", In an angiogram, this artery clearly depicts the anteroinferior border of the heart.
Click on the image for a larger depiction. Here is a link to the article on the "obtuse margin" of the heart.
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