What does a Real Heart Look Like?Dissecting a Porcine (Pig) HeartThe pig heart is interesting to us because it is very similar to the human heart in anatomy, size and function. Itsexcellent availability in most areas of the world, along with the similarities to the human heart, make porcineheart tissue ideal for transplant into humans. Of course, untreated porcine tissue would be rejected very quicklyby the recipient's body, in the same way that a human's donated organ would be rejected. To prevent this,porcine heart valves are treated with glutaraldehyde to reduce their immunogenicity. The muscle of your heart is called the myocardium. Most of the myocardiumis located in the ventricles which are roughly the size of your fist. Theporcine heart, like a human heart, has four chambers and four valves. Bloodflows through the pig heart in the same manner as through a human's. Thispicture shows the pig heart from the front, with the portion on the right of thepicture being the left side of the heart and vice versa. The aorta is clearlyvisible at the top, with an atrium on either side, while the ventricles are in thebottom left. A top view shows the aortic and pulmonary arteries as well asthe pulmonary veins and superior vena cava. Ok, let's get dirty!The first incision - Studying the right side of the heartThe first incision is along the right ventricle, allowing us to see inside the right side of the heart.The right ventricle can be identified by squeezing the heart, since the myocardium on the rightside is much less rigid than that of the left ventricle. This incision allows us to see the tricuspidvalve and the right ventricular outflow tract which includes the pulmonary valve.Longitudinal cut through the right ventricleThe right ventricle has been cut open from the apex of the heart (at the bottom) towardsthe top. In this picture, the myocardium is being held back. My finger is stuck underneathone leaflet of the tricuspid valve, which leads to the pulmonary valve. The tricuspid valve (39k JPEG)The tricuspid valve allows blood to flow from the right atrium (above) into the rightventricle when the heart is relaxed during diastole (di-a-stol-ee). When the heart beginsto contract the heart enters a phase called systole (sis-toll-ee), and the atrium pushesblood into the ventricle. Then, the ventricle begins to contract and blood pressure insidethe heart rises. When the ventricular pressure exceeds the pressure in the atrium, thetricuspid valve snaps shut. The valve itself consists of three leaflets that are attached tothe myocardium directly at the top. At the bottom, long thin fibers of collagen (a connective tissue protein)called chordae tendinae connect the leaflets to specialized heart muscles called papillary muscles. The chordaetendinae keep the valve leaflets in the right position so that they can close properly during systole.The right outflow tract (54k JPEG)Behind the posterior leaflet of the tricuspid valve is the right ventricular outflow tract. Thisleads up to the pulmonary valve and pulmonary artery. When the ventricles contract, bloodis forced along the outflow tract and through the pulmonary valve. Then the blood flows tothe lungs where gas exchange takes place.The pulmonary valve (41k JPEG) When the heart is contracting during systole, the pulmonary valve is openbecause the blood pushes the cusps out of the way. However, at the end ofsystole, the ventricles begin to relax and the intra-ventricular pressure drops.When the ventricular pressure drops to below the pulmonary artery pressure,the pulmonary valve closes and prevents back-flow (called regurgitation) ofblood into the ventricle.In the two top views, the valve has been cut away from the top of the right ventricle by an incision through themyocardium below the valve. The valve consists of three cusps, which are thin flaps of connective tissue.Because of the shape of the cusps, the pulmonary valve is described as being semi-lunar. The cusps look likelittle sacs that are attached to the wall of the pulmonary artery. Continue on with the porcine heart dissection.Heart Valve Lab Home PageRevision: 2 created on 1997/07/25 15:21:47Contacting the