BACKGROUND: Spontaneous echo contrast (SEC) of the left atrium (LA) is associated with increased risk of thromboembolism in patients with mitral stenosis(MS). The determination of the presence and severity of LA spontaneous echo contrast(SEC) is of prognostic importance in these patients. Harmonic imaging(HI), a novel echocardiographic technique that differs from conventional fundamental imaging(FI) by transmitting ultrasound at one frequency and receiving at twice the transmitted frequency, produces better endocardial border definition and myocardial opacification. However, there are no data about its value on the detection of LA SEC. The purpose of this study was to investigate the utility of transthoracic noncontrast HI in the detection of LA SEC in patients with. METHODS: Seventy-four consecutive patients with MS (49 female, mean age 51) underwent standard transthoracic echocardiograms (TTE) in both HI and FI and transesophageal echocardiography (TEE) to determine the presence and severity of LA SEC. LA SEC was graded by TEE; mild if only seen at high gain, severe if visible in the entire LA at normal gain control of the equipment. Control subjects comprised of 30 patients randomly selected from patients who did not have LA SEC at TEE examination. RESULTS: Atrial fibrillation was found in 46 patients (62.2%). The mean mitral valve area and mean mitral gradient were 1.0+/-0.3cm2 and 8.2+/-4.1mmHg, respectively. Nine patients (12.2%) had episodes of systemic embolism; stroke in 8 and peripheral embolism in 1. LA thrombus was found in 11 patients (14.9%) by TEE. LA SEC was present in all but one patient by TEE (mild in 35, severe in 38 patients). FI of TTE, however, revealed LA SEC in only 5 (6.8%) of the 73 patients. In contrast, in HI, LA SEC could be detected in 63 (86.3%) of the 73 patients. In the detection of severe LA SEC, the sensitivity of FI and HI were 13.2% (5/38) and 100% (38/38), respectively. LA SEC was not observed in control subjects either by FI or HI. CONCLUSION: Transthoracic HI significantly enhances the detection of LA SEC in patients with MS.