Virtual Cardiac Laboratory

During the laboratory experience, your primary task be to examine the images of the heart, supplied by Primal Pictures through the HSHSL.

Overview

As you work your way through this tutorial, remember the following about the heart's function. Terms you will need to identify during the virtual lab are in bold.

Valve Function & Heart Sounds

Normally, the two heart sounds are heard during each cardiac cycle through a stethoscope placed on the chest.

A soft, low-pitched third heart sound is often heard about one-third of the way through diastole in normal young individuals. It is due to the period of rapid ventricular filling during diastole.

As you work your way through this virtual lab, try to visualize the "anatomy-in-action" causing the first and second heart sounds. Remember, the tricuspid and bicuspid valves close almost simultaeously as pressure increases rapidly in the right and left ventricles, respectively, at the beginning of systole. Notice how the papillary muscles and chordiae tendinae would tug on the closing tricuspid and bicuspid valves to prevent them from entering (or prolapsing) into the atrial chambers.

Also, the pulmonary and aortic semilunar valves close almost simultaneously at the end of systole as the pressue within the relaxing ventricles decreases rapidly and the pressure within the pulmonary arteries and aorta becomes higher than ventricular pressure. The cusps of the aortic valve is thicker and "tougher" than the atrioventricular (AV) valve cusps. This causes them to seal more tightly without the anatomic assistance needed for the AV valves.

The major, but certainly not the only, cause of abnormal heart sounds is disease of the cardiac valves. When the orifice of a valve is narrowed (stenosis), blood flow through it in the normal direction is accelerated and turbulent, resulting in an abnormal heart sound. When a valve is incompetent and does not seal properly, blood flows backward through it (regurgitation or insufficiency) resulting in an abnormal heart sound. The delicate nature of the tricuspid and bicuspid valves make them especially vulnerable to injury or disease which interferes with their proper sealing. The timing of a particular murmur in relation to the mechanical events of the cardiac cycle is a valuable part of the diagnosis of the cause of a murmur.

Ventral View of the Heart

Click on and explore the image below to see if you can identify the following structures:

Dorsal View of the Heart

The image below shows the dorsal view of the heart. Click and explore with your mouse to identify the following:

  • The left and right ventricles
  • The left and right atria
  • The sinunatrial nodal artery (a coronary artery)
  • The superior and inferior vena cava

Dorsal View of the Heart (Atria Removed)

The image below shows a dorsal view of an actual heart with the atria removed. Click with your mouse and explore the image to identify the following structures:

  • The pulmonary semilunar valve
  • The aortic semilunar valve
  • The bicuspid valve
  • The tricuspid valve

The Right View of the Heart (opened)

The following images show right-side views of an actual heart with the myocardium cut away from the right ventricle and the right atrium respectively. Click and explore the first to see if you can identify:

  • Two for the three cusps of the tricuspid valve
  • The cordae tendinae ("heart strings") that hold the tricuspid valve in place
  • The papillary muscles, from which the cordae tendinae originate

Explore the following image of the right atrium to identify where the superior vena cava enters the atrium.

Wall & Septal Structures

In the image below (which is not interactive), notice the difference in thickness between the outer walls of the right ventricle and the much thicker left ventricle.

An illustration of the heart walls and septum

Also notice the interventricular septum. The interventricular septum is the major dividing wall between the right and left ventricles. It participates in the contraction and contains the AV bundle and the right and left bundles of His, which conduct depolarization to the Purkinje fibers in ventricular muscle.

A much thinner interatrial septum separates the right and left atria. The AV node is in the lower part of teh interatrial septum. The fetal ciculation includes an opening (foraman ovale) through which blood can pass from the right atria to the left atria, thus bypassing the lungs. This opening normally closes at birth, but if it remains open, surgery is necessary to repair the resulting atrial-septal defect.