The increasing use of transgenic mouse models for investigating the mechanisms of cardiac growth and function has made it important to develop noninvasive methods for assessing murine cardiac anatomy, size, and function. At present, murine cardiac mass can be determined only at necropsy. Left ventricular (LV) function can be assessed by use of various catheterization techniques, but these approaches are usually terminal procedures and provide no information about chamber anatomy and dimensions. Although transthoracic echocardiography has been used to study the LVs of rats and larger animals, the considerably smaller LV masses and somewhat faster heart rates of mice pose significant challenges to obtaining good-quality echocardiograms. In this study we tested the hypothesis that transthoracic echocardiography can image the murine LV as well as provide assessments of LV mass and function. Our results in a series of 33 mice, including normal, transgenic, and aortic-banded subgroups, demonstrate the capability of transthoracic two-dimensionally directed M-mode echocardiography in mice to (1) obtain good-quality images, (2) produce estimates of LV mass having good correlations with directly determined LV mass in normal mice, (3) detect LV hypertrophy noninvasively in different experimental models, and (4) identify impaired LV systolic function. Thus, echocardiography appears to be a promising approach for noninvasively assessing LV mass and function in mice.