Doctors are injecting a bit of the bubbly into people's veins to get a better view of their hearts.

The bubbly, in this case, is a sugar solution agitated with ultrasonic waves to create microscopic bubbles, no larger than red blood cells. In the bloodstream, these bubbles can be tracked with sound waves to reveal blood flow through the heart.

"Previously, despite their microscopic size, many . . . bubbles did not pass through the lungs, meaning we couldn't get a good image of overall blood flow in the heart," Dr. Steven Feinstein of the University of Chicago told a recent meeting of the American Heart Association. The new, smaller bubbles pass through, however.

Bubbles are needed because sound waves don't bounce cleanly off of blood itself. On the television screen used to monitor blood flow, they look like a white cloud. The pictures can be used, along with other methods of viewing the heart, to help determine whether heart surgery is necessary.

Thus far, Feinstine's bubbles have been brought to the heart through a catheter, a long tube snaked through a blood vessel. But animal studies suggest a simple injection also would work.

The bubbles, which go away by themselves, are small enough to pass through the body's capillaries, the smallest blood vessels. The largest of the bubbles is about 0.0004 inches in diameter. About 1,000 would fit on the period that ends this sentence.