We compared fundamental and tissue harmonic transthoracic echocardiographic imaging for the delineation of the left atrial appendage (LAA) in 32 subjects. The LAA images recorded in the parasternal short-axis view were divided into 4 segments and 2 observers independently graded for each segment using a visual scoring system ranging from 0 to 3 (0 = no, 3 = clearly visible over the entire length of the segment). For the 128 segments, the averaged segment scores were significantly increased after switching to harmonic imaging (1.32 +/- 0.69 versus 1.60 +/- 0.81 for fundamental and tissue harmonic imaging, respectively; P <.0005 for observer 1, and 1.38 +/- 0.65 versus 1.61 +/- 0.82, respectively; P <.001 for observer 2). In a patient with LAA thrombus, the image contrast of the thrombus was improved in harmonic compared with fundamental imaging. These data suggest that tissue harmonic imaging significantly improves image quality of the LAA.