An apparatus for determining a medical condition of a human subject, the apparatus comprising: a control unit; and a means for providing pulse wave data representative of a heart beat of the human subject; wherein the control unit is configured to perform the steps of: receiving the pulse wave data; selecting a portion of the pulse wave data indicative of a plurality of heart periods; determining a second and a third index, each of the second and third indexes being based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, wherein the third index is different from the second index; and determining a medical condition of the subject based on the second and third indexes; wherein determining the second index comprises: determining a tachogram indicative of a variability of a plurality of respiratory rate intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, determining a frequency distribution of respective respiratory rate intervals of the plurality of respiratory rate intervals, determining an entropy value based on the frequency distribution, and determining the second index based on the entropy value; and wherein determining the third index comprises: determining a plurality of beat-to-beat intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, and determining the third index based on the plurality of beat-to-beat intervals. a control unit; and a means for providing pulse wave data representative of a heart beat of the human subject; wherein the control unit is configured to perform the steps of: receiving the pulse wave data; selecting a portion of the pulse wave data indicative of a plurality of heart periods; determining a second and a third index, each of the second and third indexes being based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, wherein the third index is different from the second index; and determining a medical condition of the subject based on the second and third indexes; wherein determining the second index comprises: determining a tachogram indicative of a variability of a plurality of respiratory rate intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, determining a frequency distribution of respective respiratory rate intervals of the plurality of respiratory rate intervals, determining an entropy value based on the frequency distribution, and determining the second index based on the entropy value; and wherein determining the third index comprises: determining a plurality of beat-to-beat intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, and determining the third index based on the plurality of beat-to-beat intervals. receiving the pulse wave data; selecting a portion of the pulse wave data indicative of a plurality of heart periods; determining a second and a third index, each of the second and third indexes being based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, wherein the third index is different from the second index; and determining a medical condition of the subject based on the second and third indexes; wherein determining the second index comprises: determining a tachogram indicative of a variability of a plurality of respiratory rate intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, determining a frequency distribution of respective respiratory rate intervals of the plurality of respiratory rate intervals, determining an entropy value based on the frequency distribution, and determining the second index based on the entropy value; and wherein determining a tachogram indicative of a variability of a plurality of respiratory rate intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, determining a frequency distribution of respective respiratory rate intervals of the plurality of respiratory rate intervals, determining an entropy value based on the frequency distribution, and determining the second index based on the entropy value; and determining the third index comprises: determining a plurality of beat-to-beat intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, and determining the third index based on the plurality of beat-to-beat intervals. determining a plurality of beat-to-beat intervals based on the pulse wave data of the portion of the pulse wave data indicative of a plurality of heart periods, and determining the third index based on the plurality of beat-to-beat intervals.