The relative ability of M-mode echocardiography (EC) and systolic time intervals (STIs) to quantify acute positive inotropic interventions (PI) concurrently validated by hemodynamic measurements is unknown. Thus we studied the response of eight patients with normal coronary arteriography and LV function to successive incremental infusions of dobutamine (D-1, D-2) during cardiac catheterization. During D-1 with heart rate, arterial pressure and LV end-diastolic pressure unchanged, dP/dt max increased 65% (p less than or equal to 0.001), QS2 decreased 12% (p less than or equal to 0.01), PEP decreased 24% (p less than or equal to 0.01), LVET and PEP/LVET were not significantly changed, while EC %delta D and mean Vcf increased by 22% and 33% (both p less than or equal to 0.01). During D-2 with heart rate increased (increases 33%, p less than or equal to 0.001), EC Vcf (increases 66%, p less than or equal to 0.01) and PEP (decreases 33%, p less than or equal to 0.001) exhibited the greatest changes of the noninvasive parameters. The observed decreases in QS2 and LVET but not PEP were considerably attenuated after normalization for heart rate. Our data suggest: (1) echo and STIs are complementary in assessing PI; (2) PEP is more sensitive than QS2 in quantitating PI, particularly when large increases in contractile enhancement have occurred; and (3) both noninvasive techniques are less sensitive than dP/dt in detecting positive inotropic action.