Cardiac performance in infants referred for extracorporeal membrane oxygenation. We performed cardiac evaluations in 59 infants referred for severe lung disease to determine whether cardiac performance was impaired in those requiring extracorporeal membrane oxygenation (ECMO). Infants were divided into two groups: group 1 (n = 25) received conventional therapy and group 2 (n = 34) received ECMO therapy after meeting established criteria. Ventilatory and oxygenation indexes and estimates of right ventricular systolic pressure were measured. Load-dependent and load-independent echocardiographic indexes of cardiac performance were also measured. The infants in the two groups had similar diagnoses, age, weight, inotropic support, ventilator and oxygenation indexes on admission, and survival. Heart rate and estimates of preload and afterload were similar in the two groups. Ventricular shortening fraction was 36.1 +/- 7.6% in group 1 and 40.5 +/- 8.8% in group 2 (p value was not significant). Velocity of circumferential fiber shortening (VCF/sec) was 1.41 +/- 0.35 in group 1 and 1.58 +/- 0.39 in group 2 (p value was not significant). The relationship between wall stress and ventricular shortening was similar in the two groups. There were no differences in cardiac output. Pulmonary artery pressure was estimated to be 56 +/- 13 mm Hg in group 1 and 63 +/- 10 mm Hg in group 2 (p = 0.017). Thus no significant differences were found in load-dependent or load-independent measures of cardiac performance in infants with severe lung disease treated with ECMO or conventional therapy. We conclude that cardiac failure is not the primary cause of clinical deterioration in infants with severe lung disease who require ECMO therapy. 