Ventricular arrhythmias are frequent, sometimes complex and severe, in primary hypertrophic cardiomyopathy. They carry a poor prognosis. Some workers have reported that these arrhythmias are more common in patients with abnormal myocardial perfusion. Other groups have underlined the important role of the sympathetic nervous system in the development of ventricular hypertrophy and the genesis of ventricular arrhythmias. Therefore, a population of 28 patients with primary hypertrophic cardiomyopathy (PHCM) were studied by thallium 201 myocardial scintigraphy and sympathetic innervation was assessed using a structural analogue of noradrenaline, meta-iodobenzyl-guanidine (MIBG). Then, perfusion and innervation were correlated with ventricular arrhythmias observed on 24 hours holter monitoring electrocardiogram. Perfusion abnormalities were observed in 60% of patients: stable in mild left ventricular hypertrophy, labile in severe left ventricular hypertrophy. They were not related to the presence of muscular bridges and systolic compression of septal arteries demonstrated by coronary angiography. These perfusion abnormalities were closely correlated to ventricular extrasystoles observed on Holter monitoring. In this series, and compared to controls, the fixation of MIBG as determined by the Heart/Mediastinum (H/M) ratio was significantly decreased (2.27 +/- 0.31 versus 2.57 +/- 0.33 in controls). Uniform myocardial uptake of MIBG with no defect or significant global hypofixation was observed in 32% of PHCM. Regional and occasionally global hypofixation was observed in 68% of patients. In moderate hypertrophy, reduced uptake was not uniform, the lateral wall and apex being the most abnormal. Uptake of MIBG was significantly correlated to septal wall thickness and to left ventricular mass index. These defects were related to abnormal neuronal uptake of MIBG.(ABSTRACT TRUNCATED AT 250 WORDS)