Desensitisation of the -adrenoreceptors (-AR) may contribute to a post-exercise reduction in left ventricular (LV) function. However, attenuation of the chronotropic and inotropic responses to a -AR agonist may depend upon alterations in parasympathetic tone. Furthermore, changes in cardiac output (Q) and LV diastolic function in response to a -AR agonist, pre- to post-prolonged exercise, remain unclear. Seven trained males (mean ± SD, age 27 ± 6 years) performed 4 hours of ergometer rowing. Peak heart rate (HR) and LV systolic and diastolic functional responses to incremental isoproterenol infusion (2, 4 and 6 ìgkgmin-1) were assessed after vagal blockade (glycopyrrolate, 1.2 mg). LV systolic function was assessed by the pressure/volume ratio (systolic blood pressure/end systolic volume) and Q, whilst diastolic function was evaluated as peak early and late transmitral filling velocities. Following exercise, the pressure/volume ratio decreased by 25% (P<0.05), whereas Q was unchanged (P>0.05). The early/late filling ratio was reduced by 36% after exercise, due to an elevation in late LV filling (P<0.01). The increase in HR response to isoproterenol infusion was blunted post-exercise at both 4 and 6 ìgkgmin-1 (127 ± 7 and 132 ± 6 beats.min-1) compared to pre-exercise (138 ± 8 and 141 ± 12 beatsmin-1, P<0.05). Additionally, the pressure/volume ratio and Q were blunted post-exercise in response to isoproterenol (P<0.05). In contrast, diastolic function was similar before and after exercise during isoproterenol infusion (P>0.05). Desensitisation of the -adrenoreceptors contributes to an attenuation in left ventricular systolic but not diastolic function following prolonged exercise.