This is an illustration of a particular perspective in a cardiac echocardiogram. An “apical view” is one of the four views of an echocardiogram, and you get it by aiming the little probe between the fifth and sixth ribs on the left side of your body, aimed a little bit upward (toward your head) and a bit outward (toward your armpit). It’s a way of looking at your left ventricle, left atrium, and mitral valve. The left atrium is where oxygenated blood enters the heart before the left ventricle sends it out to the rest of the body.
This illustration, showing different areas of the heart muscle, was done in 2006 as part of a series of heart illustrations for Yale’s med school by Patrick J. Lynch, medical illustrator, with C. Carl Jaffe, MD, cardiologist. I found it in the Lynch collection on Wikimedia Commons.