We studied 23 DMD and eight BMD patients using cardiac echo, 24 h ECG and positron emission tomography (PET) with the radiotracers N-13 ammonia and F-18 fluorine deoxyglucose. The ECG was abnormal in 23 cases with alterations in the PR and/or QT intervals, abnormal Q waves in the lateral leads and ST segment depression. Twenty-four hour ECG showed that patients were more likely to produce premature ventricular ectopic beats with advancing age and 17 patients had paroxysmal ST segment depression. LV function was normal or mildly reduced in 24 cardiac echoes. PET studies were visibly abnormal in 15 patients. Regional perfusion defects involving the apex, lateral or anterior left ventricular walls were present, nine cases demonstrated a corresponding increase in glucose metabolism. Three out of 15 demonstrated matched perfusion/metabolism defects. One BMD had severe LV dilation with globally poor perfusion and metabolism. The abnormalities seen with PET were confirmed with both quantitative and semi-quantitative analysis of radioactive counts. Similar results were obtained for both DMD and BMD, where both groups demonstrated significant regional perfusion/metabolism mismatches. We have shown a reduced uptake of N-13 ammonia which is indicative of a reduction in myocardial perfusion. The use of N-13 ammonia to measure perfusion has been validated in animal studies. PET with either N-13 ammonia- or oxygen labelled water can be used to measure myocardial perfusion. We chose N-13 ammonia as this was most readily available to us.