<p>　Background: Cardiac function can affect vascular function as well as peripheral hemodynamics. Increases and decreases in cardiac afterload due to vasoconstriction and vasodilation can influence cardiac contractility and rhythm considerably. There are some reports that increased reflected waves from peripheral arterial sites could lead to exacerbation of ischemic heart disease in patients with hypertension. It is important to elucidate precisely the relationship between cardiac function and cardiovascular hemodynamics.</p><p>　Objectives: The purpose of this study was to analyze the relationship between cardiac contractility, circulatory dynamics, and augmentation index (AI) changes when afterload was changed by vasoactive drug administration.</p><p>　Methods: Fifteen normal Japanese white rabbits, aged 10-12 months, were anesthetized with intravenous administration of pentobarbital sodium (30 mg/kg) and fixed in a supine position. A catheter-tip pressure transducer and an ultrasonic flow probe were placed on the ascending aorta under spontaneous respiration. Angiotensin II (Ang II, 20-40 μg/kg/min) and sodium nitroprusside (NTP, 20-30 μg/kg/min) were infused into the ear vein to change cardiac afterload until the mean arterial pressure (MAP) reached 140 and 80 mmHg, respectively. Pressure and flow waves at the ascending aorta were simultaneously recorded by echocardiography before and after the infusion of either Ang II or NTP. Cardiac contractility was assessed by fractional shortening (FS) of the left ventricle.</p><p>　Results: When Ang II was administered, systolic blood pressure (SBP), diastolic blood pressure (DBP), MAP, amplitude of the late systolic wave (S₂) ( ＝ pulse pressure; PP), total peripheral vascular resistance (TPR), augmentation pressure (Aug P; ＝ S₂ － S₁) and AI were increased significantly, whereas stroke volume (SV), aortic compliance (SV/PP) and FS of the left ventricle were decreased significantly. There was no significant change in cardiac output (CO) or amplitude of the early systolic wave (S₁) due to the infusion of either Ang II or NTP. When NTP was administered, SBP, DBP, MAP, S₂ (PP), TPR, Aug P and AI were decreased significantly. CO and SV showed a tendency to decrease, while SV/PP demonstrated a trend to increase, although these trends were not statistically significant.</p><p>Regarding S₁ and FS, little change was observed. FS showed significant negative correlations with SBP, DBP, MAP, S₂ (PP), TPR, Aug P and AI, and a significant positive correlation with SV/PP.</p><p>　Conclusion: We conclude that cardiac contractility was largely associated with changes in the reflected waves from peripheral arterial sites due to changes in vascular tone.</p>