The purpose of this study was to evaluate the effect of sequential external counterpulsation (SECP) on cerebral and renal blood flow. The effect of SECP on carotid and renal artery blood flow was studied in 35 and 18 patients, respectively. With a portable unit, cuffs were applied to the calves and thighs, sequentially inflated with air at the onset of diastole, and deflated at the onset of systole. Carotid and renal artery Duplex studies were performed during intermittent SECP. Flow velocity and flow velocity integral were measured at baseline and during SECP. Diastolic augmentation of carotid and renal artery flow velocity was observed in all patients. The mean carotid flow velocity integral increased by 22% from 27.7 ± 1.8 cm to 33.1 ± 2.3 cm ( P = 0.001). The mean renal artery flow velocity integral increased by 19% from 21 ± 1 cm to 25 ± 1 cm ( P = 0.0001). With SECP, a new diastolic Doppler flow velocity wave was observed, with an average peak carotid diastolic flow velocity of 56 ± 4 cm/sec and an average peak renal artery diastolic flow velocity of 40 ± 2.5 cm/sec. This diastolic wave was 75% (carotid) and 68% (renal) as high as the systolic wave during SECP. In addition, with SECP the systolic wave increased by 6% and 8% in the carotid and renal artery, respectively ( P = 0.02 and 0.006, respectively). In conclusion, SECP significantly increases carotid and renal blood flow. This noninvasive, harmless treatment may be useful to support patients with decreased cerebral and renal perfusion.