There is a need to monitor perfusion of the microcirculation in patients with minimal invasive approaches. The recent development of ultrasound contrast agents may open such an opportunity and permit to visualize online perfusion of cardiac muscle and other organs. An effective approach to achieve this objective is with gas filled microbubbles that provide strong ultrasound wave reflection and scatter. To interpret the ultrasound scattering profiles, it is necessary to understand the transport of microbubbles in the microcirculation, specifically their transport in blood stream, the attachment to blood cells and endothelium, as well as possible leakage across the microvascular wall. Each of these events provides an opportunity to monitor with ultrasound not only microvascular blood flow but also detect inflammatory sites in the circulation.