Death from accidental electrocution is generally thought to be due to an arrhythmia, but little is known of the anatomic changes in the heart and almost nothing is known about the conduction system itself. We have studied the hearts of four men who died from electrical accidents and directed particular attention to the coronary arteries, conduction system, and neural structures of the heart. In every heart there was widespread focal necrosis involving all the myocardium and including the specialized tissue of the sinus and atrioventricular nodes. In all four hearts there was contraction band necrosis of smooth muscle cells in the tunica media of the coronary arteries. Cells in the His bundle and bundle branches were less affected. Neural structures of the heart were minimally involved. We also sought any cardiac changes of a chronic nature that may have predisposed to a fatal arrhythmia. Two of the four hearts were slightly enlarged, and increased myocardial mass predisposes to ventricular fibrillation and makes it more difficult to revert. One heart exhibited focal fibromuscular dysplastic narrowing of small coronary arteries, including that artery supplying the coronary chemoreceptor. Another heart had fatty deposition extensively present within and around the sinus and atrioventricular nodes. Thus numerous abnormalities specifically attributable to the electrocution help explain the pathogenesis of the electrical instability known to occur. But in three of the four hearts there were also chronic abnormalities favoring electrical instability but predating the electrocution.