A 42-year-old male patient, previously in good health, developed signs of pericarditis, pericardial effusion and possible myocarditis 3 weeks after a virus infection of the upper respiratory tract. Because of enlargement of the previously normal cardiac silhouette, an M-mode-echocardiogram was performed. A pericardial effusion and pericardial thickening was diagnosed. Disproportionate septal thickening was noted (septum/posterior wall = 1.4). 3 days after institution of cortisone therapy gradual clinical improvement started. on day 6 a repeat M-mode-echocardiogram showed regression of the pericardial effusion of the septal thickening. Consecutive echocardiograms showed complete disappearing of the pericardial effusion, regression of the pericardial thickening, and complete normalisation of the left ventricular dimensions. Computer-assisted analysis of the first echocardiogram revealed reduced rate of septal and posterior wall thinning and prolongation of the early diastolic period of rapid filling, while peak VCF remained within normal limits. These changes were much less apparent on day 6. On day 26 all relaxation- and contraction parameters were within normal limits. It is concluded that in this case transient disproportionate thickening of the interventricular septum, prolongation of the early diastolic period of rapid left ventricular filling and reduced rate of diastolic septal and posterior wall thinning may have represented edematous and/or inflammatory changes of the myocardium. It is supposed that these findings may represent early changes in acute peri-myocarditis.