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Description / Table of Contents: Summary Dobutamine stress echocardiography (DSE) leads to strong hypercontraction, tachycardia, and peripheral vasodilatation. In previous studies systolic obstruction of the left ventricular outflow tract (LVOT) was observed as a result of these factors. To evaluate left ventricular function and morphology in patients (pts) with induced systolic LVOT obstruction, we used continuous wave (CW) doppler registrations in combination with quantitative 2-D-echocardiography in 100 pts during routinely performed DSE (5–40 μg/kg/min). In addition left ventricular wall thickness was measured. Symptoms were registrated using a standardised questionaire and cardiac arrhythmias were counted over a two minute intervall at rest and during the maximal heart rate of each patient. During DSE dynamic flow acceleration with late systolic peak velocity above 2 m/second (s) was considered to represent LVOT obstruction in pts with normal flow profiles in the LVOT before infusion of dobutamine. For invasive studies pts were investigated with femoral catheterisation by the method of Judkins. A greater than 50% stenosis was judged to be significant. Results: Examinations in 73 pts provided data of sufficient quality for echocardiographic and Dopplersonographic evaluations. 39 pts, 26 men, 13 women, mean age 64 ± 8 years, developed late systolic flow velocities above 2 m/s and therefore formed the obstructive group (grp A). Grp B consisted of 34 pts, 26 men and 8 women, mean age 66 ± 10 years, who showed normal time velocity integrals during DSE. In 41 pts invasive data provided information concerning the existence and severity of coronary artery disease. There were no significant differences in the increase of heart rate, the product of maximal systolic blood pressure and maximal heart rate or the percentage of pts, who reached their age corrected submaximal heart rate during DSE. Obstructive pts (group A) showed late systolic dynamic acceleration of systolic flow with a mean maximal speed of 315.4 ± 139.8 cm/s, which peaked 0.12 ± 0.04 s after the R-wave. From the velocities we calculated a mean pressure gradient of 47.5 ± 39.7 mm Hg using the modified Bernoulli equation. Group B patients showed lower and earlier maximal speeds with a mean value of 158.2 ± 37.6 cm/s, 0.09 ± 0.04 s after the R-wave, corresponding to a pressure gradient of 10.6 ± 4.9 mm Hg (p 〈 0.001). Ejection fractions were higher (p 〈 0.001) before the test in grp A: 68.2 ± 8% compared to 55.7 ± 10.4% in B. This difference increased during peak stress: 74.1 ± 7.7% compared to 59.5 ± 12.8%. Enddiastolic (EDVI) and endsystolic volume indexes (ESVI) were lower in grp A (p 〈 0.001). During DSE, the decrease in ESVI was somewhat stronger for pts in grp A. Left ventricular hypertrophy was more often seen with obstruction. Septal thickness was increased in A: 1.45 ± 0.34 cm compared to 1.13 ± 0.27 cm in B (p 〈 0.001). Left ventricular posterior wall measured 1.03 ± 0.28 cm in A and 0.83 ± 0.23 cm in B (p 〈 0.01). 27 pts in grp B and only 9 in grp A had a history of previous myocardial infarction. Showing no difference at rest, wall motion score indexes raised under DSE in both groups and developed significantly higher scores in grp B at peak stress: 1.30 (1.0–1.90) compared to 1.18 (1.0–1.90) compared to 1.18 (1.0–1.75) in A. We observed typical chest pain more often in grp B. Unspecific symptoms and arrhythmogenic complications were not statistically different, with the exception of ventricular bigeminy which was more often observed in grp B. A decline in the diastolic blood pressure was observed in pts with very severe obstruction (〉 3.5 m/s, p 〈 0.05). Sensitivity of DSE was 84%, specificity 79%. No significant differences between pts with and without obstruction were observed. Summary: Intraventricular obstructions during DSE are often observed in pts with normal systolic function at rest and during peak stress, especially in the case of left ventricular hypertrophy. This flow pattern is not regularly correlated to clinical signs, symptoms or complications. It did not impair diagnostic accuracy concerning the detection of significant coronary artery disease in our pts.