Discussion Four cases of sustained cardiac arrhythmia in familial periodic paralysis have been reported, of which only one occurred in a patient with hypokalemic periodic paralysis (Klein et al. 1963, Levitt et al. 1972, Lisak et al. 1972). Rarely an arrhythmia may occur transiently in induced attacks of periodic paralysis (Gass et al. 1948, Scherf & Schott 1973). The sustained arrhythmia is unrelated to attacks of paralysis and consists of ventricular extrasystoles or tachycardia, frequently bidirectional in nature. It has previously been found resistant to treatment, although quinidine may reduce the frequency of the arrhythmia and acetazolamide prevent sudden death (Klein et al. 1963, Levitt et al. 1972, Lisak et al. 1972). Our patient was converted from ventricular fibrillation with DC shock and showed good response to lignocaine and mexiletene. As with the cases of Klein et al.(1963) and Lisak et al.(1972), the ECG was improved by both oral and intra-venous potassium but did not correlate with changes in theserum potassium. We also believe the insertion of an epicardial pacemaker to be of particular value in themanagement of certain arrhythmias, such as this, by reducing the risk of drug-induced asystole.