Although slightly affected by alterations in preload, the maximum first derivative of left ventricular pressure with respect to time, Max(dP/dt), is widely regarded as a simple and convenient index of cardiac contractility for clinical use. The feasibility of noninvasive, hence repeatable, measurement of Max (dP/dt) will certainly lead to re-evaluation of its usefulness. Max(dP/dt) is given by the following equation: Max(dP/dt)=ρc Max(du/dt), where ρ is the blood density, c the pulse wave velocity, and u the flow velocity in the aorta. This equation has been previously validated in animal experiments and has now been applied to the clinical setting for the first time. In 20 patients without aortic stenosis, left ventricular pressure was measured with a catheter-tip micromanometer, aortic ejection flow velocity was measured by Doppler echocardiography, and pulse wave velocity by mechanocardiography or Doppler echocardiography. Then, δc Max (du/dt was calculated from the measured data and compared with measured Max (dP/dt). A significant positive correlation was found between them (ρc Max (du/dt) = 0.96 x Max (dP/dt) + 6.52, r=0.83, p<0.001.) In 11 patients with hypertension, ρc Max (du/dt) was obtained before and after long-term (average 13.1 months) treatment with antihypertensive drugs. In spite of the expected reduction in blood pressure and the regression of left ventricular mass, ρc Max (du/dt) remaioned unchanged. In 9 patients with dilated cardiomyopathy, the effects of β1 -agonist were tested at the beginning of therapy (30 mg/day denopamine) and 6 months later. The increase in ρc Max (du/dt) observed 1 hour after oral administration of he drug had not changed significantly 6 months later. We conclude that the index ρc Max (du/dt), is useful in assessing the contractile state of the left ventricle noninvasively.