To further investigate the dependency of strain and strain rate on changes in preload, afterload, and heart rate, these variables are consecutively changed prior to drug administration. For this purpose, all patients first have their baseline data recorded, thereafter are paced at two different rates, then preload and afterload is altered by passive leg elevation and phenylephrine, respectively. Hemodynamic and echocardiographic data are collected simultaneously at baseline and after each intervention. Before administration of the drugs, baseline conditions are restored.