BACKGROUND The effect of the posture of semirecumbent patients on the hemodynamics and performance of intra-aortic balloon (IAB) were studied in vivo and in vitro. METHODS An IAB was inserted into a glass tube filled with saline, fully inflated and deflated using an intra-aortic balloon pump (IABP). Three successive cycles were filmed at 125 frames/s with the tube positioned at various angles...