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Objectives. Acoustic quantification (AQ), a recently developed ultrasonic integrated backscatter imaging system providing on-line measurements of ventricular cavity areas and their functional indexes, was validated in comparison to angiography and Doppler derived systolic dP/dt. Normal AQ-reference values were established. Methods and Results. 1. In 45 patients undergoing heart catheterization, AQ derived areas in end-diastole (EDA), end-systole (ESA) and the resulting fractional area change (FAC) in apical 2- and 4-chamber view were compared to the corresponding biplane angiographic data. All correlations yielded significant values (p<0.0001; EDA: r=0.90, SEE=2.6 cm2; ESA: r=0.91, SEE=2.2 cm2; FAC: r=0.90, SEE = 4.1%). However, AQ-areas were underestimated by about 25%. 2. In 36 patients with mitral regurgitation AQ-FAC and AQ derived systolic dA/dt were compared to the Doppler derived systolic dP/dt, yielding significant correlations with r=0.91 and r=0.87; p<0.0001. 3. In 50 healthy subjects, AQ derived EDA, ESA and FAC averaged 25.7 ± 4.9, 14.7 ± 3.3 cm2and 43.2 ± 4.8% for the left, and 17.1 ± 3.8, 9.0 ± 2.9 cm2and 47.3 ± 9.2% for the right ventricle. For EDA normalized peak filling (PFR) and ejection rates (PER) yielded 2.7 ± 0.28 and -2.4 ± 0.42 EDA/sec for the left and 3.4 ± 0.74 and -2.9 ± 0.62 EDA/sec for the right ventricle. The interobserver and day-to-day variability of AQ in healthy subjects and cardiac patients was low for EDA, ESA and FAC (<12%) and higher for PFR and PER (<20%). Conclusion. In comparison to angiography AQ reliably quantitates on-line left ventricular fractional area change, although AQ- areas are underestimated. AQ offers reproducible values of systolic and diastolic function and a new approach to cardiac patients.