by Richard E. Moon, Richard D. Vann and Peter B. Bennett
This 640 x 415 pixel image shows that venous blood (blue) is separated within the normal heart from arterial blood (red) being pumped to the tissues, resulting in almost all the venous bubbles being trapped by the lung capillaries. At least 10 percent of the population, however, has a small opening, known as a patent foramen ovale, between the left and right atria. It can allow bubbles to cross into the arterial system, through which they may cause damage in the brain and other organs.