Dissecting a heart is one of the most hands-on ways to learn how blood moves through the body. Whether you’re working with a sheep, pig, or cow heart in a biology class, the process follows the same basic steps: orient the heart, open each side, and identify the chambers, valves, and vessels inside. Here’s a clear walkthrough from setup to cleanup.
What You Need Before You Start
A preserved mammalian heart is the standard specimen. Sheep and pig hearts are the most common in school labs because they’re close in size and structure to a human heart. You can order them from biological supply companies, and they often come vacuum-sealed in preservative fluid.
For tools, you’ll want dissection scissors (preferred over a scalpel for most cuts), a scalpel with a fresh blade for precise incisions, a dissection tray, and pins to hold tissue back as you work. A blunt probe is useful for exploring vessels and valve openings without tearing anything.
Safety matters more than most students realize. Wear chemical-resistant gloves, a lab apron, and safety glasses for the entire dissection. Work in a well-ventilated room. No eating, drinking, or gum chewing while specimens are out. Always cut away from your body and away from other people, and never hold the specimen in your hand while cutting. Wash your hands frequently, and be mindful that once your gloved hand touches the specimen, it’s contaminated. Avoid touching your face or adjusting your glasses with dirty gloves.
Orienting the Heart
Before making any cuts, spend a few minutes figuring out which side is which. This step saves confusion later. Place the heart on the tray with the rounded, bulging front (anterior) side facing you. The pointed tip at the bottom is the apex, and the flat top where the large vessels emerge is the base. Most of the apex tilts slightly to the left, which mirrors how the heart sits in the chest.
Now identify left and right. Remember that the heart’s left and right are reversed from your perspective when it’s facing you, just like looking at another person. The left ventricle is the side with the thicker, firmer wall. You can squeeze both sides gently to feel the difference. The right ventricle feels noticeably thinner and softer. On the surface, look for the coronary arteries and veins, which appear as pale or darker lines running through the fat along grooves in the muscle. A diagonal groove running from the upper right to the lower left marks the boundary between the two ventricles (the interventricular sulcus). A horizontal groove near the top separates the atria above from the ventricles below.
At the base, you’ll see the major vessels. The large, firm-walled vessel slightly to the right of center (from your view) is the aorta. Next to it, the softer, thinner vessel is the pulmonary trunk. On the back side, the pulmonary veins enter the left atrium, and the superior and inferior vena cava enter the right atrium.
Opening the Right Side
Start with the right side of the heart because its thinner wall is easier to cut through. Insert your scissors into the superior vena cava (the large vein entering the top of the right atrium) and cut downward through the atrial wall and into the right ventricle, continuing toward the apex. Open the wall like a flap and pin it back.
Inside the right atrium, the walls are relatively smooth on one side but have a ridged, comb-like texture on the other. These ridges are called pectinate muscles. Look for the opening of the inferior vena cava at the bottom and the smaller opening of the coronary sinus, which drains blood from the heart muscle itself.
Between the right atrium and right ventricle, you’ll see the tricuspid valve, named for its three thin, translucent flaps (cusps). These flaps are anchored to the ventricle wall by thin, white, string-like cords called chordae tendineae. These cords connect to small mounds of muscle on the ventricle wall known as papillary muscles. During each heartbeat, the papillary muscles contract and pull on the chordae tendineae, which prevents the valve flaps from being pushed backward into the atrium when the ventricle squeezes. You can tug gently on the chordae tendineae with a probe to see how they hold the valve in place.
The inner wall of the right ventricle has irregular muscular ridges called trabeculae carneae, giving it a rough, textured appearance compared to the smoother atrium. At the top of the right ventricle, find the opening to the pulmonary trunk. Inside it sits the pulmonary valve, which has three small, pocket-shaped cusps. These are semilunar valves (named for their crescent shape) and look quite different from the tricuspid valve. They don’t have chordae tendineae. Instead, they open and close passively with blood flow.
Opening the Left Side
Now cut into the left side. Insert your scissors into a pulmonary vein on the back of the heart and cut down through the left atrium and into the left ventricle toward the apex. Pin the wall open.
The first thing you’ll notice is wall thickness. The left ventricle wall is dramatically thicker than the right. In a human heart, the left ventricular wall measures about 1.2 to 1.5 cm at autopsy, compared to just 0.3 to 0.5 cm for the right ventricle. That’s roughly three times thicker. The reason is straightforward: the right ventricle only needs to pump blood to the lungs (a short trip), while the left ventricle pumps blood to the entire body, requiring far more force.
Between the left atrium and left ventricle sits the mitral valve (also called the bicuspid valve), which has two flaps instead of three. Like the tricuspid valve, it’s anchored by chordae tendineae and papillary muscles. The chordae tendineae on the mitral side tend to include a few especially thick, strong cords called strut chordae, which bear the greatest mechanical load during each heartbeat. You’ll also see fan-shaped cords at the edges where the two leaflets meet, which act like hinges to bring the flaps together during closure.
At the top of the left ventricle, find the opening into the aorta. Inside it is the aortic valve, another set of three semilunar cusps that look similar to the pulmonary valve. Just above the aortic valve cusps, look for two small openings in the aorta wall. These are the coronary artery openings, where blood first branches off to feed the heart muscle itself.
The Interventricular Septum
With both sides open, examine the thick muscular wall dividing the left and right ventricles. This is the interventricular septum. It’s nearly as thick as the left ventricular free wall because it functions as part of the left ventricle’s pumping machinery. Run your probe along both sides. The septum is solid muscle, which is what keeps oxygen-rich and oxygen-poor blood completely separate. In a healthy heart, there’s no opening between the two ventricles.
Tracing Blood Flow Through the Specimen
Once everything is open, use a probe to trace the complete path blood takes. Start at the superior vena cava, pass through the right atrium, through the tricuspid valve into the right ventricle, up through the pulmonary valve into the pulmonary trunk (heading to the lungs), then return via the pulmonary veins into the left atrium, through the mitral valve into the left ventricle, and out through the aortic valve into the aorta. This double-loop system is why the heart is essentially two pumps fused together, each handling one circuit.
If you can, insert your probe into the coronary artery openings just above the aortic valve and gently see how far it travels along the heart’s surface. This is the heart’s own blood supply, and it’s the first blood that branches off from the aorta with every beat.
Cleanup and Disposal
When you’re finished, clean all instruments with a detergent solution, rinse with water, and dry thoroughly. Remove scalpel blades carefully and discard them in a sharps container, not in regular trash. Double-bag the specimen along with used gloves and disposable aprons in opaque garbage bags. Your teacher or lab manager will handle final disposal, which typically involves a contracted waste service for animal tissue. Wipe down your dissection tray and work surface with disinfectant, and wash your hands thoroughly before leaving the lab.