The pathophysiological mechanisms responsible for increased cardiovascular mortality in diabetic autonomic neuropathy are unknown. To investigate the effect of autonomic neuropathy on myocardial function, we performed dynamic contrast-enhanced magnetic resonance perfusion imaging during baseline conditions and after Dipyridamole-induced vasodilatation in nine type 1 diabetic patients with autonomic neuropathy (AN+), defined by cardiovascular tests, as well as in 10 type 1 diabetic patients without autonomic neuropathy (AN-) and 10 healthy control subjects. Baseline myocardial perfusion index (K(i)) was similar in the three groups (AN+ 88.6 +/- 8.7 ml. 100 g(-1). min(-1), AN- 82.6 +/- 7.2, control subjects 93.7 +/- 9.0) (means +/- SE). K(i) during Dipyridamole vasodilatation was significantly lower in the patients with autonomic neuropathy (P < 0.001) than in the other groups (AN+ 131.1 +/- 13.0 ml. 100 g(-1). min(-1), AN- 177.3 +/- 8.6, control subjects 197.2 +/- 8.9). Mean blood pressure was unchanged during Dipyridamole infusion in AN- and control subjects, whereas a significant blood pressure decrease was found in AN+ (15.6 +/- 2.6 mmHg, P < 0.025). There was a significant correlation between blood pressure response to Dipyridamole and myocardial perfusion reserve index. We conclude that type 1 diabetic patients with autonomic neuropathy have a decreased myocardial perfusion reserve capacity when challenged with a vasodilatator, a finding that may in part be the pathophysiological substrate for the increase in mortality in these patients. The underlying mechanism may be defective myocardial sympathetic vasodilatation, a lack of ability to maintain blood pressure during vasodilatation, or both.