through the cardiovascular system. These forces demonstrate themselves to the clinician as paired values of blood flow and blood pressure measured simultaneously at the output node of the left heart. Hemodynamics is a fluidic counterpart to the Ohm's law in electronics: pressure is equivalent to voltage, flow to current, vascular resistance to electrical resistance and myocardial work to power. The relationship between the instantaneous values of aortic blood pressure and blood flow through the aortic valve over one heartbeat interval and their mean values are depicted in Fig.1. Their instantaneous values may be used in research; in clinical practice, their mean values, MAP and SV, are adequate. Blood flow parameters Systemic (global) blood flow parameters are (a) the blood flow per heartbeat, the Stroke Volume, SV [ml/beat], and (b) the blood flow per minute, the Cardiac Output, CO [l/min]. There is clear relationship between these blood flow parameters: CO[l/min] = (SV[ml] × HR[bpm])/1000 {Eq.1} where HR is the Heart Rate frequency (beats per minute, bpm). Since the normal value of CO is proportional to body mass it has to perfuse, one "normal" value of SV and CO for all adults cannot exist. All blood flow parameters have to be indexed. The accepted convention is to index them by the Body Surface Area, BSA [m2], by DuBois & DuBois Formula, a function of height and weight: BSA[m2] = W0.425[kg] × H0.725[cm] × 0.007184 {Eq.2} The resulting indexed parameters are Stroke Index, SI (ml/beat/m2) defined as SI[ml/beat/m2] = SV[ml]/BSA[m2] {Eq.3} and Cardiac Index, CI (l/min/m2), defined as CI[l/min/m2] = CO[l/min]/BSA[m2] {Eq.4} These indexed blood flow parameters exhibit typical ranges: For the Stroke Index: 35 < SItypical < 65 ml/beat/m2; for the Cardiac Index: 2.8 < CItypical < 4.2 l/min/m2. Eq.1 for indexed parameters then changes to CI[l/min/m2] = (SI[ml/beat/m2] × HR[bpm])/1000 {Eq.1a} Oxygen transport The primary function of the cardiovascular system is transport of oxygen: blood is the vehicle, oxygen is the cargo. The task of the healthy cardiovascular system is to provide adequate perfusion to all organs and to maintain a dynamic equilibrium between oxygen demand and oxygen delivery. In a healthy person, the cardiovascular system always increases blood flow in response to increased oxygen demand. In a hemodynamically compromised person, when the system is unable to satisfy increased oxygen demand, the blood flow to organs lower on the oxygen delivery priority list is reduced and these organs may, eventually, fail.