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Increases in Cardiac Output and Oxygen Consumption During Enhanced External Counterpulsation. BACKGROUND: Regular enhanced external counterpulsation (EECP) improves exercise capacity possibly through a training effect, but the roles of oxygen consumption (VO2) vs. direct EECP effects (diastolic augmentation, DA-ratio), and their relation to cardiac index (CI) during EECP are unknown. METHODS: We studied eight patients with angina pectoris (median [range] age 72 [53-85], 25% women), who underwent EECP for 35 daily sessions. Before, during and after the first and last sessions, we assessed VO2, DA-ratio and CI. RESULTS: At first EECP, CI increased from 2.2 (1.7-2.9) L/min/m2 prior to EECP to 3.0 (2.2-3.8) during EECP (p=0.011), and returned to 2.4 (0.8-3.0). Similarly, VO2 increased during EECP and returned to baseline after EECP. These patterns were reproduced at the last EECP session. Absolute values of CI and VO2 correlated with each other during but not prior to or after EECP. The increase in CI correlated with the increase in VO2 by trend: (first session, r 0.52, p=0.19; second session r 0.69, p=0.09), but not with DA-ratio. CONCLUSIONS: Acutely during EECP, there is an increase in cardiac output that is unrelated to direct EECP effects but related to, and may be secondary to, an increase in peripheral O2 demand. This may represent a training effect.