SUMMARY Dangerous or long lasting ventricular arrhythmias developed in three patients who had sustained an electrical injury in which current passed through the thorax. In all three cases there was a delay of [8][9][10][11][12] hours between the injury and the onset of symptoms. The ventricular arrhythmias were severe and long lasting. In two of the three patients, ventricular tachycardia or ventricular fibrillation or both occurred and in one patient ventricular parasystole developed. No enzymatic evidence of myocardial necrosis was found but the results of an endomyocardial biopsy carried out in two of the three patients showed focal myocardial fibrosis and increased numbers of Na, K-pumps. The two patients with ventricular tachycardia became symptom free after appropriate antiarrhythmic treatment and in the third patient ventricular parasystole disappeared spontaneously within two years.Patients sustaining electrical injury in which current passes through the thorax should be monitored electrocardiographically for at least 24 hours, and patients with unexpected arrhythmias should be questioned about previous electrical injury.A lightning strike is a recognised cause of sudden death. When the mechanism of such death was investigated in 1775 it was found that an electrical shock applied to a head stunned hen whereas another shock to the sternum resuscitated it.' In 1850 it was shown in a dog that application of a current to the exposed heart was followed by very rapid and irregular movements of the ventricles-that is, probably ventricular fibrillation. We report three cases of non-fatal electrical-injury that were followed by delayed serious ventricular arrhythmias. Endomyocardial biopsy. specimens were taken from two of the patients. Microscopy showed myocardial fibrosis.The membrane bound enzyme, the Na, KATPase or Na, K-pump, performs the transport of sodium ions out of the cell and potassium ions into the cell and is essential for the specific properties of muscle and nerve tissue such as contractility and excitability. "

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