Doxorubicin (DXR) is one of the most effective antineoplastic agents, but its use is limited by its myocardial toxicity. Myocardial injury reduces the cyclic variation of integrated backscatter (CV-IBS) and so the present study was designed to investigate whether CV-IBS can be used to detect the early phase of myocardial damage in patients receiving DXR. Thirty-four subjects constituted the study population, none of whom showed clinically evident heart failure. CV-IBS was obtained for both the interventricular septum and the left ventricular posterior wall in the parasternal short-axis view. Standard echographic measures of left ventricular function were also made. Subjects without DXR exposure or evident cardiac diseases served as controls. The total dose of DXR administered per patient was 339±164 mg/m² (range: 95-680 mg/m²). Conventional echographic parameters, including left ventricular wall thickness, dimensions, fractional shortening, and ejection fraction, showed no significant differences between the 2 groups. In contrast, CV-IBS was significantly decreased in the DXR group compared with the control group (septum: 4.7±1.7 vs 7.2±1.9 dB, p<0.0001; posterior wall: 6.7 ±2.2 vs 8.0±1.6 dB, p<0.05). CV-IBS can be used as an early indicator of DXR-induced myocardial damage in patients demonstrating normal left ventricular systolic function. (Circ J 2003; 67: 929 - 933)