The frequencies of electrocardiographic (ECG) abnormalities and myocarditis were determined, retrospectively, among 154 cases of trichinellosis [101 males and 53 females, with a mean (S.D.) age of 35.60 (14.64) years] who were hospitalized at the University Hospital for Infectious Diseases in Zagreb, Croatia, over a 5-year period. Eighty-seven (56%) of the patients, most of them in the invasive phase of infection with Trichinella spiralis, were found to have abnormalities when examined by 12-lead, resting electrocardiography. The ECG disorder most frequently observed was a non-specific ventricular repolarization disturbance (with ST-T wave changes), followed by bundle-branch conduction disturbances, and sinus tachycardia. The other ECG disorders recorded, during various phases of the infection, were sinus bradycardia, right bundle-branch block, supraventricular and ventricular extrasystoles, low-voltage QRS complexes in standard limb leads, first-degree atrio-ventricular block, and atrial fibrillation. Eighteen (12%) of the patients were identified as cases of myocarditis (13 in the invasive phase and five in the convalescent) and two (1.3%) as cases of myopericarditis. One patient developed acute myocardial infarction 28 days after the onset of disease and died soon thereafter; an autopsy revealed multiple necroses and fibroses of the myocardium and thrombus of a coronary artery. Although ECG abnormalities appear to be a common feature of trichinellosis, especially during the invasive phase of the disease, they are rarely associated with a poor prognosis. A transient, non-specific, ventricular-repolarization disturbance is the abnormality most commonly observed.