A family of miniaturized axial flow pumps has been developed, including the Hemopump, the 14-F, and the 21-F HP, which were especially designed for cardiological use. We designed an experimental set-up to study the unloading properties of these devices in a model of regional stunning in an anesthetized, open thorax preparation in sheep. Stunning was caused by 15-min occlusion of the diagonal branch of the left anterior descending coronary artery with subsequent 90 min of reperfusion. Regional myocardial function was assessed by sonomicrometry. A control group was compared with 2 groups with either mechanical unloading during part of ischemia (Group 2) or the early phase of reperfusion (Group 3). In either unloading protocol, both Hemopumps were used. It was shown that recovery from asynchrony was significantly faster in Groups 2 and 3 if unloading was performed with the 21-F HP compared with control Group 1 and the groups using the 14-F HP (p > 0.05). Thus, mechanical unloading with the 21-F Hemopump enhances recovery from stunning whereas unloading with the 14-F HP has only minor effects on hemodynamics and no effects on recovery.