Techniques for noninvasive imaging of specific disease-related molecular changes are being developed to enhance diagnosis and therapeutic decision making in the clinical setting, and to facilitate research efforts. Molecular imaging with contrast-enhanced ultrasonography relies on the detection of the acoustic signal produced by microbubble or nanoparticle agents that are targeted to sites of disease. This Review describes the basis for ultrasound molecular imaging, the unique features of contrast agent behavior or detector performance in relation to clinical or research needs, and the progress that has been made to date in imaging key events in cardiovascular medicine, such as atherosclerosis, postischemic inflammation, angiogenesis, transplant rejection and thrombus formation.