1. A method for determining a beat-to-beat stroke volume or a cardiac output based on at least one measurement of arterial pressure data, the method comprising the steps of: obtaining at least one measurement of arterial pressure data using a measurement unit; providing the at least one measurement of arterial pressure data to a processor; and causing the processor to perform the steps of: computing a compliance or impedance in dependence of at least one measurement of arterial pressure data using a non-linear model, said non-linear model being given by the following equation: 
 A ( p )= Am (0.5+(1/π)arctan(( p−p 0)/ p 1), wherein A(p) is the pressure-dependent cross-sectional area of the aorta in cm 2 , Am is the maximal area of the aorta at very high pressure; p 0 is a parameter indicating an inflection point of a pressure curve A(p); and pl is a parameter describing a half-width of the pressure curve; using said compliance or impedance in a pulse contour method for determining the beat-to-beat stroke volume or cardiac output based on the measured arterial pressure data; approximating parameters of the non-linear model based on a further model based on a person-specific characteristic; using the approximated parameters for the non-linear model; and computing the aortic compliance for an effective pressure, wherein for the effective pressure a mean pressure during systole is selected that is computed beat-to-beat for a contraction frequency of the heart.