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QW 3600 (EchoGen®) (EG) is a new ultrasonic contrast agent which produces intense LV cavity and even myocardial opacification following IV injection in animals. However, no data exists regarding the potential of this agent to be used in conjunction with stress echo in humans. Therefore, in 17 normals we compared the results of injecting equal volumes of normal saline and progressive doses of EG: 0.02 cc/kg (5 pts). 0.05cc/kg (4). and 0.1cc/kg (8) during stress echo performed to 85% of maximal heart rate. Echo was performed in apical 4 chamber view, and LV contrast opacification was assessed qualitatively (1 + weak and incomplete, 2+ complete cavity. 3+dense and complete) and by videodensitometry (0.3cm2) region of interest in mid cavity. All subjects tolerated the injections well without adverse events. No significant changes were observed in pulse oximetry, the ECG, or 25 laboratory studies. We analyzed the maximal change (Δ) in systolic (S) and diastolic (D) pressure (mmHg) and heart rate (HR) and peak videointensity (PVI) from baseline to post exertion following the injection of either saline or EG (Table, all p=NS for saline vs EG except PVI)DoseSalineEGΔHRΔSBPΔDBPPVIΔHRΔSBPΔDBPPVI0.0248431813424917280.0537351611434321420.13740191037441962LV opacification was absent with saline, was inconsistent at 0.02 and 0.05cc/kg doses, but was≥ 2+ in all but one 0.1cc/kg administration (mean 2.4). Peak LV videointensity after EG was 62 for 0.1cc/kg. Thus, EchoGen® is a new contrast agent which is well tolerated when used with stress echo in normals and results in complete LV opacification at a dose of 0.1cc/kg. EchoGen® should prove to be a useful adjunct to clinical stress echo.