Because of the development of gene knockout and transgenic technologies, small animals, such as mice and rats, have become the most widely used animals for cardiovascular imaging studies. Imaging can provide a method to serially evaluate the effect of a particular genetic mutation or pharmacologic therapy (1). In addition, imaging can be used as a noninvasive screening tool for particular cardiovascular phenotypes. Outcome measures of therapeutic efficacy, such as ejection fraction, left ventricular mass, and ventricular volume, can be determined noninvasively as well. Furthermore, small-animal imaging can be used to develop and test new molecular imaging probes (2,3). However, the small size of the heart and rapid heart rate of murine models create special challenges for cardiovascular imaging.