The cardiovascular effect of doxorubicin (DOX) was investigated in a Sprague Dawley (SD) rat model in vivo which allowed continuous cardiovascular hemodynamic monitoring, and serial blood sample collection for measurement of RBC concentrations of ATP. The rats were randomly divided into 2 groups. Group A (n = 8) received DOX 10 mg/kg in normal saline by subcutaneous (sc) injection twice daily for 4 doses. Group B (n = 11) received the same injections with normal saline. Blood samples (0.3 mL each) were obtained from each rat before the last injection (Time 0), and at 0.05, 0.25, 1, 1.2, 1.5, 2, 3, 4, 5 and 6 hours after the injection. Hemodynamic recording was collected continuously throughout the experiment. Difference of response between groups was considered significant at p < 0.05 (t-test). The systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) before the last DOX dose vs control (in parenthesis) were 119 ± 7 (vs 123 ± 11 mmHg), 87 ± 12  (vs 104 ± 11 mmHg, p < 0.05), and 386 ± 27 (vs 378 ± 48 bpm), respectively. The blood pressure fell gradually after the last injection in both groups, and by the end of the experiment the SBP was significantly lower in the DOX treated group (85 ± 9 vs 103 ± 15 mmHg, p < 0.05). There was no difference in the red blood cell (RBC) concentrations of ATP between the DOX treated rats and control (1.52 ± 0.53 vs 1.69 ± 0.44 mM, p > 0.05). The results suggest that DOX decreased blood pressure but had little effect on HR or RBC concentrations of ATP.