We studied 17 consecutive patients of Dengue Haemorrhagic Fever/Dengue Shock Syndrome (DHF/DSS) to assess cardiac function by radionuclide ventriculography, echocardiography and electrocardiography (ECG) during the epidemic of Dengue virus type-2 (DEN-2) in Delhi, India (1996). Case definitions laid down by the WHO were followed. Fourteen patients were seropositive for Dengue infection. In radionuclide ventriculography study, the mean left-ventricular ejection fraction was 41.69 (5.04% (range 33-49%) and 7 patients had an ejection fraction less than 40%, global hypokinesia was detected in 12 (70.59%) patients. In echocardiography, the mean ejection fraction was 47.06 (3.8%). Eight patients had Dengue Shock Syndrome and the mean ejection fraction was 39.63% (4.97% in radionuclide ventriculography, out of which 5 patients had an ejection fraction below 40%. To find out the nature of myocardial involvement, 99m Tc-pyrophosphate imaging was done in 4 patients and it was discontinued further because no myocardial necrosis was detected in those patients. Five patients had ST and T changes in the electrocardiogram, radionuclide ventriculography and echocardiography revealed no abnormalities after 3 weeks of follow up and the ejection fraction was more than 50% in all cases. Global hypokinesia also improved and ECG changes reverted back to normal within 3 weeks. Acute reversible cardiac insult may be noticed in Dengue Haemorrhagic Fever/Dengue Shock Syndrome and could be responsible for hypotension/shock seen in some of these patients. Further studies are required to establish the pathogenic mechanisms of cardiac dysfunction in patients with Dengue Haemorrhagic Fever/Dengue Shock Syndrome.