We evaluated the effects of acetylstrophanthidin on baroreflex sensitivity in patients soon after an acute myocardial infarction. Baroreflex control of heart rate is frequently depressed after acute myocardial infarction and few data are available as to the effects of pharmacological intervention on this parameter. The reflex chronotropic response to arterial baroreceptor stimulation was assessed in 29 patients with uncomplicated acute myocardial infarction in control conditions (72-96 h after symptom onset) and 30 min after acetylstrophanthidin administration. To check for spontaneous baroreflex sensitivity variations, 24 patients with the same characteristics were evaluated at the same time intervals before and after a 10-cc bolus of saline placebo. Baroreflex sensitivity was assessed by calculating the regression line relating phenylephrine-induced increases in systolic blood pressure to the attendant changes in RR intervals. Mean baseline baroreflex sensitivity value for the whole study population was 7.4 +/- 4.5 ms/mmHg and was unchanged, 7.0 +/- 4.5 ms/mmHg, after acetylstrophanthidin (P = NS). Mean baroreflex sensitivity values were also comparable dividing patients according to the site of infarction both before and after acetylstrophanthidin. Despite the lack of difference in mean baroreflex sensitivity values between the two studies, at a post hoc analysis an inverse relation was found in the total study population between baseline baroreflex sensitivity values and their changes after acetylstrophanthidin (r = -0.62; P < 0.005). The inverse relation was also evident separately in anterior (r = -0.57; P < 0.05) and in inferior (r = -0.70; P < 0.005) myocardial infarction patients.(ABSTRACT TRUNCATED AT 250 WORDS)