Hey there, welcome back to Cardiac Anatomy! I'm Emily Dawson and, as always, I'm joined by the brilliant Dr. Eleanor Whitfield.Hello, everyone. It’s wonderful to be back. Today, we’re diving into probably the most critical “gatekeepers” in the heart—the valves. And Emily, I think our listeners will find this installment especially practical, especially after our big-picture look at cardiac structure last episode.Yes! Last time, we kinda touched on the valves as part of the overall chamber tour. But today, let’s really focus on the four main ones: the mitral, tricuspid, aortic, and pulmonic valves. So, the basics—there are two atrioventricular valves and two semilunar valves, right?Precisely. The atrioventricular valves—the mitral and tricuspid—separate the atria from the ventricles. The mitral valve is on the left, between the left atrium and left ventricle, and the tricuspid is on the right—between the right atrium and right ventricle.Yep, and switching to the semilunar valves—that’s the aortic and pulmonic valves. The aortic valve connects the left ventricle to the aorta, while the pulmonic valve sits between the right ventricle and the pulmonary trunk. Honestly, I used to get so mixed up on which is left and which is right…Okay, this is kinda silly, but the way I finally memorized it—I was like, “Mitral has an ‘M’ for ‘Man, that’s the left side!” And ‘tricuspid’ and ‘tricycle’ both have ‘tri,’ so naturally, tricycle rides on the right.” It’s not perfect but, hey, if it sticks, it works!I rather like that, Emily. Anything that aids recall when you’re under pressure, I say go for it. And just to recap in one sentence: mitral and aortic equals left, tricuspid and pulmonic equals right. Got it, everyone?Absolutely. And remember, these valves aren’t just doors—they actually shape the movement of blood, keep the chambers distinct, and are literally built for the “one-way only” traffic that keeps the heart working smoothly. Super high stakes if they don’t!Let’s zoom in on the atrioventricular valves, starting with that mitral valve on the left side. It’s actually thicker than the tricuspid valve, did you know? And the orifice—the opening—measures about 9 centimeters in circumference. That’s smaller than the tricuspid, which is roughly 11 centimeters.I think what really helped me was visualizing the mitral valve sort of like a bishop’s hat—that classic little hat shape. It’s actually a great image if you’re trying to recall the anatomy during an exam!Indeed. And this valve only has two leaflets—an anterior and a posterior. The anterior leaflet is the largest cusp, sitting right next to the left and noncoronary cusps of the aortic valve, while the posterior leaflet is smaller, about one third of the size, but takes up more of the circumference of the annulus. Structurally, the surface facing the atrium is smooth, but the ventricular surface is quite irregular, with fibrous nodules—technically called Albini’s nodules—present.The papillary muscles are so crucial here too, right? They anchor those chordae tendineae—the “heartstrings”! Fun fact: the anterolateral papillary muscle supports the anterior leaflet, and the posteromedial muscle is for the posterior. They keep that valve from flipping inside out when the ventricle squeezes.Exactly, and when things go awry with that arrangement, it can have dramatic effects. Actually, several years ago, I had a patient with severe mitral valve prolapse—think dramatic billowing of those leaflets—and the resultant regurgitation was caught beautifully on 3D transesophageal echocardiography, or TEE. The leaflets weren’t coapting in the center, which led to rather severe backflow into the atrium.I saw a TEE image of that once during my rotation. It was wild. The difference with a properly working mitral valve is so striking compared to even just mild prolapse, let alone severe regurgitation. Oh, and for students: if you want to nerd out on structural heart disease videos, that’s a great area to do it!On to the tricuspid valve—which as we said, is on the right side. It has three cusps: anterior, septal, and posterior. The orifice is actually larger than the mitral, and the septal leaflet is the one neighboring the membranous septum. Chordae tendineae once again attach these cusps to three papillary muscles—one for each cusp.It’s easy to think of the tricuspid valve as just a “mirror image” of the mitral, but it’s got those three leaflets and bigger opening, so it’s definitely got its own personality! I always had to double-check diagrams for this because the septal position trips me up every time.Switching gears, let’s take a look at the semilunar valves, which are honestly just as cool as the AV valves. Both the aortic and pulmonic valves have three pocket-like cusps, and they’re both, well, literally “semilunar”—kind of moon-shaped if you picture them in cross-section.Very true. They may look similar, but there are some key differences. The aortic valve, located between the left ventricle and aorta, has slightly thicker structure—its orifice is around 7.5 centimeters, a bit less than the pulmonic valve which is about 8.5 centimeters. The aortic valve’s three cusps are called right, left, and noncoronary. The right and left cusps are especially memorable because that’s where the coronary arteries originate; it’s a crucial clinical point if you’re interpreting imaging or planning surgeries.Yeah—don’t forget those sinuses of Valsalva! They’re these cool pouch-like structures just behind the aortic valve that help the cusps function and, yeah, play a role in how the coronaries fill during diastole. I always highlight that for students because it’s a huge ‘aha moment’ when they spot it on a cross-section.Both semilunar valves also share these central thickened nodules—called nodules of Arantii—and the way the cusps meet during closure forms little crescentic curves called lunulae. The leaflets are convex from below. The endothelial lining of these valves merges almost seamlessly with the arteries they lead into, creating a perfect passage from ventricle to vessel.I gotta share this: the first time I spotted the nodules of Atlantii in a pulmonary valve repair, I did a double take—I thought I’d found something pathologic. And then, my attending was like, “Nope, that’s normal!” The pulmonary valve, by the way, sits a bit in front of the aortic valve, and those thin cusps are super delicate. It’s at practically a right angle to the aortic valve when closed, which feels like a trick question on anatomy quizzes!You’re absolutely right. The pulmonary valve’s anatomy makes it unique—not just for position but the thinner, more fragile leaflets, and those nodules of Atlantii. It’s also located anterior and superior to the other three cardiac valves. And, as with the aortic valve, it opens in systole and closes in diastole, helping keep the blood flow properly routed out to the lungs.Okay, that’s a ton of detail packed in, but honestly, reviewing these valves by their shapes, associations, and little quirks really helps them stick. This is what makes reviewing cardiac anatomy kinda fun, at least for me!Absolutely—and that’s why we’re here: to make these details both memorable and usable, whether you’re prepping for exams or just want to understand how the heart’s elegant plumbing works. Well, Emily, I think we’ve given our listeners a hearty dose of valve knowledge for today.Definitely. Thanks for tuning in, everyone, and we’ll be back soon with even more heart nerd goodness. Eleanor, always a pleasure chatting valves with you!Likewise, Emily. Goodbye, and goodbye to all our listeners—keep those heart diagrams handy and stay curious!

Episodes

Mastering Cardiac Valves