In hemodialysis patients, large arteriovenous (AV) fistulas for vascular access may cause ventricular hypertrophy and high-output cardiac failure. The long-term cardiac consequences of functional AV fistulas in renal transplant patients are unclear. A precise knowledge of these consequences is important to decide if and when such fistulas should be closed in successfully transplanted patients. In this retrospective study including 61 stable renal transplant patients with adequate renal function (serum creatinine <2.0 mg/100 ml), echocardiography was performed in 39 patients with a functional AV fistula (group 1) and in 22 whose fistulas had been closed, for esthetic reasons, within 2 months postoperatively (group 2). The volume flow of the fistulas, measured in 22 randomly selected individuals of group 1, was 900 ± 350 ml/min (range 500–1,600). Patients of group 1 were older (40 ± 12 vs. 33 ± 12 years, p < 0.05), had longer duration of the fistula (62 ± 31 vs. 36 ± 30 months, p < 0.05), higher body mass index (24 ± 4 vs. 22 ± 3 kg/m<sup>2</sup>, p < 0.05), systolic (154 ± 24 vs. 138 ± 18 mm Hg, p < 0.05) and diastolic (96 ± 12 vs. 89 ± 11 mm Hg, p < 0.05) blood pressure and increased left ventricular (LV) end-diastolic dimension (53 ± 5 vs. 49 ± 5 mm, p < 0.01). LV mass, cardiac index, ejection fraction and the proportion of patients with LV hypertrophy were comparable in the two groups. LV end-diastolic dimension was positively and independently influenced only by the presence of the AV fistula (p < 0.01) after adjusting for age, duration of the fistula, body mass index, systolic and diastolic blood pressure and the nature of the antihypertensive drugs used. In conclusion, the persistence of large, high-flow AV fistulas for prolonged periods of time had little impact on cardiac morphology and function of stable renal transplant patients with adequate renal function. The data do not support routine closure of these fistulas in all renal transplant patients.