Abstract: The invention relates to a method and an apparatus for determining the systolic phase interval (SP) of an arterial pressure curve with a starting point (t0) of the systolic phase interval (SP) and an end point (tN) of the systolic phase interval (SP) wherein a QT interval is defined as the start of the Q wave and the end of the T wave in the hearts electrical cycle and wherein the determination of the end point (tN) of the systolic phase interval (SP) is restricted to the measured points of arterial pressure which fulfill the condition that the difference in time between the end point (tN) to be determined of the systolic phase interval (SP) and the starting point (t0) of the systolic phase interval (SP) is smaller than the QT interval.