(3.31)

In this cut-away dissection we can see the outflow tract of the left ventricle from the side. Here's the aortic valve. We've left intact part of the anterior cusp of the mitral valve, along with the chordae tendineae and papillary muscles. The anterior cusp of the mitral valve forms part of the wall of the outflow tract, so blood flows past it this way in diastole and this way in systole.

Here's the anterior cusp of the mitral valve in motion, with the mitral valve opening below it, and the outflow tract above it.

Now that we've seen both ventricles, we'll move on to look at the two outflow valves, the pulmonary valve and the aortic valve, and also at the pulmonary trunk and the first part of the aorta.

Here are the two ventricles, dissected so that we can see the outflow valves. Here's the aortic valve, here's the pulmonary valve. Each has three cusps. The pulmonary trunk and the aorta are markedly dilated at their origins. On each vessel the dilatation consists of three bulges, or sinuses, whose position matches the position of the valve cusps.

To get a better look at the cusps of the outflow valves we'll remove these parts of the vessel walls. Each cusp of an outflow valve is shaped like one third of a parachute. Here the cusps are hanging loose. Each cusp has a delicate free border which closes against those of its neighbors.

Here's the pulmonary valve in motion. In diastole, back-pressure closes the valve abruptly, the three cusps pressing against each other to meet exactly at a point.

Here's the aortic valve. It works in just the same way. Here's the opening of the right coronary artery, which we'll see in a minute. The left one is out of sight down here.

Now that we've seen the outflow valves, we'll move on, to look at the two major outflow vessels, the aorta and the pulmonary trunk. To see them we'll go to a more intact dissection. The pulmonary trunk passes backwards to the left of the aorta, then divides into the left pulmonary artery, and the right pulmonary artery.

The right pulmonary artery curves around above the left atrium, passing behind the root of the aorta, and behind the superior vena cava. This early branch supplies the superior lobe of the right lung.

This cord is the divided ligamentum arteriosum, the remnant of the ductus arteriosus which connects the pulmonary trunk and the aorta in intra-uterine life.

Here's the aorta. It starts to the right of the pulmonary trunk. Its beginning is well hidden in the epicardial fat. In front of it is the right atrial appendage. To its right is the superior vena cava, and behind it is the right pulmonary artery.