To determine the effects of parasympathetic withdrawal or sympathetic stimulation on Doppler echocardiographic measures of left ventricular diastolic filling, we studied 10 young normal subjects aged 21 to 29 years during separate infusions of atropine (0.8 mg followed by 0.4 mg every 10 minutes until heart rate greater than 110 beats/min or a total dose of 2 mg was attained) and epinephrine (10, 25 and 50 ng/kg/min for 12 minutes each). At the highest atropine dose, heart rate increased from 60 +/- 9 to 105 +/- 8 beats/min (mean +/- standard deviation), the diastolic filling period decreased by 61% (573 +/- 141 to 222 +/- 34 ms), the peak early (E) filling decreased 23% (77 +/- 12 to 61 +/- 11 cm/s), the peak atrial (A) filling increased 103% (40 +/- 6 to 81 +/- 17 cm/s), and the E/A ratio decreased by 60% (2.0 +/- 0.5 to 0.8 +/- 0.3) (all p less than 0.001). These alterations were not correlated to changes in systolic function, preload, blood pressure or plasma catecholamines, all of which were unchanged. However, atropine-induced changes in diastolic filling period were highly correlated to changes in E peak (r = 0.64, p less than 0.01), A peak (r = -0.95, p less than 0.001) and the E/A ratio (r = 0.93, p less than 0.001). The effects of atropine on the E/A ratio were normalized by dividing the E/A ratio by the diastolic filling period (E/A/diastolic filling period).(ABSTRACT TRUNCATED AT 250 WORDS)