Pulmonary capillary wedge pressure (PCWP) is the key to describing left ventricular (LV) unloading, however, the relation between pressure and the echocardiography-derived surrogate of LV volume (left ventricular end-diastolic diameter (LVEDD)) as a function of pump speed (RPM) in continuous-flow left ventricular assist device (CF-LVAD) patients is unknown. In this study the pressure-volume relationship as a function of RPM during ramp testing was investigated by simultaneously measuring PCWP by Swan-Ganz catheter and LVEDD by echocardiography. The ramp protocol started at usual pump setting (ramp-base) and then went from 8,000 RPM (ramp-low) increasing by 400 RPM/5 minutes until reaching 12,000 RPM or suction/arrhythmic event (ramp-high). The study was finalized by a 25-Watt exercise test at two ramp steps. Ten patients with ramp-base of 9,300 ± 241 RPM (at which 3/10 had aortic valve opening) were examined. At ramp-low, ramp-base and ramp-high PCWP was 20 ± 4, 14 ± 4 and 7 ± 3 mmHg (P<0.001 for all comparisons) and LVEDD 6.6 ± 1.0, 6.7 ± 0.9 and 5.5 ± 1.7 cm (P<0.05 for all comparisons but ramp-low vs. ramp-base). Correlation between PCWP -and LVEDD-slopes; R =0.53, (P=0.02). In conclusion, PCWP as a function of RPM is weakly correlated with changes in LVEDD. Thus LVEDD is not an accurate measure of unloading in CF-LVAD patients.