Microbubble contrast visualization within the right heart is almost always due to intravenous injections containing microbubbles. In the absence of immediate administration of agitated solutions, several other mechanisms for the occurrence of echo contrast spontaneously in the cardiovascular system have been postulated. Often overlooked as a source of contrast are microbubbles from remotely injected solutions that persist in the circulation because of markedly delayed clearance. Two patients were observed with apparently spontaneous contrast detected in the right heart chambers, both of whom had congestive heart failure, tricuspid regurgitation, and pulmonary hypertension. Regardless of the exact mechanism involved, the finding of this phenomenon reflects the presence of right heart failure and a low flow state.
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