To investigate the possible causes of left ventricular dysfunction after total correction of tetralogy of Fallot, 84 patients, aged 1 1/2 to 16 years, were studied by left ventricular cineangiography both before and a mean of 4.6 months after operation. Left ventricular ejection fraction and mean velocity of circumferential fibre shortening were calculated; using multivariate analysis the results were correlated with age at operation, the degree of hypoxia and polycythaemia before operation, occurrence of hypoxic spells, and the duration of operative procedures (cardiopulmonary bypass and aortic cross clamping). The postoperative left ventricular ejection fraction was decreased slightly or moderately in 46% of patients. The variable most significantly associated with altered left ventricular function was a history of hypoxic spells. Age, the degree of chronic hypoxia, and polycythaemia did not correlate significantly with left ventricular function indices. Although no correlation was found between the duration of cardiopulmonary bypass and left ventricular ejection fraction, bypass times exceeding 120 minutes were associated with decreased ejection fractions; this was statistically significant and independent of the variable "hypoxic spells". Thus repeated episodes of acute hypoxia and long operative procedures appear to have a deleterious effect on left ventricular function in tetralogy of Fallot.