A device for determining a cardiac function parameter, the device comprising: a sonic sensor for determining timing data of a closure of a mitral valve; a pressure cuff for applying pressure to an occluded position on the brachial artery; a sensing unit coupled to the pressure cuff; characterized in that the device further comprises a processing unit configured for: determining, for each cardiac cycle, data related to a breakthrough of blood past said pressure cuff and a corresponding time value from a closing of the mitral valve, wherein the determining is based on sensor measurements from the sonic sensor and the sensing unit, and wherein each cardiac cycle is one from a plurality of cardiac cycles during deflation of the pressure cuff; fitting a target polynomial function to at least some of the measured pressure values applied by the cuff and the corresponding time values; deriving a corresponding polynomial function representing blood pressure at the aorta, based on said target polynomial function and a mathematically derived delay value representing a time shift between the target polynomial function and said corresponding polynomial function; wherein said target polynomial function is a 4 th degree polynomial denoted as ax 4 + bx 3 + cx 2 + dx + e = y and wherein said delay value is derived as: delay = 3 b + − 9 b 2 − 24 ac 12 a; and determining a value of at least one cardiac function parameter based on said corresponding polynomial function. a sonic sensor for determining timing data of a closure of a mitral valve; a pressure cuff for applying pressure to an occluded position on the brachial artery; a sensing unit coupled to the pressure cuff; characterized in that the device further comprises a processing unit configured for: determining, for each cardiac cycle, data related to a breakthrough of blood past said pressure cuff and a corresponding time value from a closing of the mitral valve, wherein the determining is based on sensor measurements from the sonic sensor and the sensing unit, and wherein each cardiac cycle is one from a plurality of cardiac cycles during deflation of the pressure cuff; fitting a target polynomial function to at least some of the measured pressure values applied by the cuff and the corresponding time values; deriving a corresponding polynomial function representing blood pressure at the aorta, based on said target polynomial function and a mathematically derived delay value representing a time shift between the target polynomial function and said corresponding polynomial function; wherein said target polynomial function is a 4 th degree polynomial denoted as ax 4 + bx 3 + cx 2 + dx + e = y and wherein said delay value is derived as: delay = 3 b + − 9 b 2 − 24 ac 12 a; and determining a value of at least one cardiac function parameter based on said corresponding polynomial function. determining, for each cardiac cycle, data related to a breakthrough of blood past said pressure cuff and a corresponding time value from a closing of the mitral valve, wherein the determining is based on sensor measurements from the sonic sensor and the sensing unit, and wherein each cardiac cycle is one from a plurality of cardiac cycles during deflation of the pressure cuff; fitting a target polynomial function to at least some of the measured pressure values applied by the cuff and the corresponding time values; deriving a corresponding polynomial function representing blood pressure at the aorta, based on said target polynomial function and a mathematically derived delay value representing a time shift between the target polynomial function and said corresponding polynomial function; wherein said target polynomial function is a 4 th degree polynomial denoted as ax 4 + bx 3 + cx 2 + dx + e = y and wherein said delay value is derived as: delay = 3 b + − 9 b 2 − 24 ac 12 a; and determining a value of at least one cardiac function parameter based on said corresponding polynomial function.