Skeletal muscle powered assist ventricles (SMV) are being investigated in animal studies as a treatment for heart failure. Muscle fatigue is almost always dependent upon muscle capillary blood flow. This study examined the relationship between SMV intrapouch pressure and blood flow to the circumferential muscle in a working SMV with a mock circulation. The unconditioned rectus abdominis muscle was used to create an in situ SMV in five dogs. Muscle blood flow was measured by both the radioactive microsphere and the electromagnetic flow probe method as the pouch pressure was varied between 10 and 70 mmHg and as the SMV was stimulated to contract at a rate of 20 min-1. The correlation coefficient for the two methods was 0.908. At pouch pressures of 10, 40, and 70 mmHg, the respective blood flow values were 22.60 ± 2.50 (1 SEM), 12.20 ± 2.10, and 4.40 ± 0.74 ml min-1 (p < 0.05). When they were corrected for muscle weight, the mean blood flow values at these same pouch pressures were 0.28 ± 0.03, 0.15 ± 0.03, and 0.05 ± 0.01 ml min-1 g-1, respectively (p < 0.05). SMV output was measured for each pouch pressure that was tested. Pouch output, expressed as ml min-1, was 458 ± 20 (1 SEM) at an SMV diastolic pouch pressure of 10 mmHg, 309 ± 22 at a pouch pressure of 40 mmHg, and 103 ± 6 at a pouch pressure of 70 mmHg. It was concluded that blood flow to unconditioned rectus abdominis muscle decreases as SMV intrapouch pressure increases and that this effect is associated with decreased SMV output. This study also shows good correlation between two different methods of determining blood flow.