"Pharmacologic" stress testing with inotropic stimulation is useful in the detection of coronary artery disease when ventricular dysfunction is provoked. However, abnormal diastolic filling may be masked or mimicked because of the influence of aging, heart rate, and loading conditions. We evaluated age effects on left ventricular filling at rest in young (n = 5) and old (n = 6) purebred beagles that were free of occlusive coronary disease and left ventricular hypertrophy, and we also evaluated age-related differences in left ventricular filling velocities in response to dobutamine and phenylephrine. Pulsed Doppler echocardiography of left ventricular filling velocities was performed at baseline and then after the administration of dobutamine (10 to 20 micrograms/kg/min) infusion. Repeat baseline recordings were obtained and then phenylephrine was administered intravenously in doses of 5 to 25 micrograms/kg/min until systolic arterial pressure increased by at least 30 mm Hg above baseline. At baseline, Doppler echocardiography revealed that there were no significant differences in the early (E) velocity or velocity time interval (VTI), and atrial (A) velocity or the A/E velocity ratio between the young and old groups. However, the A VTI and the A/(A + E) VTI ratio were significantly increased in the old group. With dobutamine administration, the E velocity did not significantly increase from baseline in either group. The E VTI, A velocity and A VTI increased significantly in both groups, but the increases were not different between groups. With phenylephrine infusion there was a significant decrease in the E VTI in the old group but neither the A/E velocity or the A/(A + E) VTI ratio significantly changed from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)