The relation between left ventricular mean systolic pressure (LVSP) determined by planimetric integration and systolic and diastolic pressure measured in a peripheral artery (SAP and DAP) was calculated using data published by Ross & Braunwald in 1964. The relation was LVSP = SAP-0.32 +/- 0.06 (s.d.) X (SAP-DAP). The formula SAP- 0.32 (SAP-DAP) was used to calculated LVSP, and the correlation between measured and calculated LVSP was found to be 0.91 (P less than 0.001). It is concluded that LVSP can be calculated with reasonable accuracy from measurements of arterial pressure in patients without aortic stenosis. At present three different formulas are in use for the calculation of left ventricular stroke work index (LVSWI). The pressure work is defined as SAP, LVSP or mean arterial pressure minus mean pulmonary capillary wedge pressure or left ventricular end diastolic pressure. This makes comparisons between different studies with respect to LVSWI difficult or impossible.