Cardiac function was assessed in 11 children with end-stage chronic renal failure (CRF) by a prospective longitudinal study. Left ventricular performance was determined noninvasively by mechanocardiographic determination of systolic time intervals during three consecutive stages of the disease: on conservative treatment (CT), on regular hemodialysis (HD) and after successful renal transplantation (TP). The mean ratio of the pre-ejection period to left ventricular ejection time (PEP/LVET) was slightly increased on CT (0.33) compared to normal (0.29), and markedly increased 6 and 12 months after start of HD (0.38 and 0.40, respectively), indicating impairment of left ventricular performance which was clinically undetectable. 12 months after TP mean PEP/LVET was normal (0.31). The upper normal limit of PEP/LVET was exceeded by two children on CT, seven at 12 months after start of HD and by two children 12 months after TP, respectively. It is concluded that subclinical forms of uremic heart disease are common in children on HD and tend to resolve after TP.