We previously demonstrated stability of ventricular volumes and cardiac function in normal and in chronically failing mouse hearts in MR systems with a vertical-bore magnet for up to 1 h. However, in order to exploit the benefits of an increased magnetic field strength of these MR systems in more time-consuming studies required by, for example MR spectroscopy, we investigated whether cardiac function and ventricular volumes of healthy and infarcted mice would be affected in vertical position over a prolonged period. We applied high-resolution MR cine imaging on an 11.7 T vertical MR system to monitor cardiac functional parameters of normal and chronically failing mouse hearts over a period of 3 h in an upright position, with a temporal resolution of < or =15 min. We monitored left-ventricular volumes and cardiac functional parameters in both groups. In normal mice, we detected a decrease of left-ventricular end-systolic volumes by 8 microl and an approximately 23% increase of ejection fraction over time indicating a small but detectable degree of orthostatic dysregulation. Observed changes were more pronounced in mice with heart failure. Despite significant changes in left-ventricular volumes and function, absolute values measured for all functional cardiac parameters are consistent with near-physiological conditions. Thus, mice can be studied in high-field MR systems positioned vertically for 3 h.