The aim of this study was to search for a cardiac cause of death after an otherwise negative medico-legal autopsy in 1,000 adults under 65 years of age with no previous history, who suffered a sudden death. Four hundred and seven coronary causes were established with 152 negative autopsies and 441 other cardiac lesions. These 441 cases comprised 193 cardiomyopathies, 106 His bundle lesions, 50 partial forms of Uhl's anomaly (or arrhythmogenic right ventricular dysplasia), 14 isolated mitral valve prolapses, 22 chronic valvular lesions, 8 myocarditis, 16 pulmonary embolisms, 11 chronic cor pulmonale, 11 aortic dissections and 10 atrophic fibrous plaques of the left ventricle, sequellae of thoracic trauma. His bundle lesions (isolated and associated) were observed 299 times out of 1,000 cases and mitral valve prolapse 125 times. Age and gender, circumstances of sudden death, the weight of the heart, are reported for each group of conditions. The frequency of associations, especially of His bundle lesions, suggests that they may have a potentialising effect on the genesis of the fatal arrhythmia.