BACKGROUND It is widely known that blood flow redistribution is impaired in patients with chronic heart failure (CHF). However, the relationship between exercise tolerance and the degree of blood flow redistribution is not fully understood. Whole-body thallium-201 chloride ((201)Tl) scintigraphy can estimate blood flow distribution. This study will evaluate the relationship between exercise tolerance and blood flow redistribution using whole-body scintigraphy in patients with CHF. RESULTS Exercise stress whole-body thallium scintigraphy was performed in 19 patients with CHF (mean ejection fraction: 33.0%; peak oxygen uptake: 15.5 ml x min(-1) x kg(-1)). Blood flow redistribution was quantified by comparing the regional thallium count (count/pixel) in the thigh and arm. We then assessed the relationship between these parameters and parameters obtained from cardiopulmonary exercise testing. (201)Thallium-chloride uptake in the thigh increased during exercise compared to rest (p<0.05), while its uptake in the arm was not different between exercise and rest. Increased (201)Tl uptake in the thigh during exercise was positively correlated with exercise tolerance (r=0.689). In contrast, (201)Tl uptake in the arm was not correlated with exercise tolerance. CONCLUSIONS By using this method, it is concluded that blood flow redistribution to the exercising muscle increases as the exercise tolerance increases in patients with CHF.