(A)Pulmonary artery and right ventricular pressure tracings in tachypacing (HF) and control (Ctrl) dogs. (B)Mean pulmonary artery pressure increased, while mean aortic pressure decreased, reflecting the secondary pulmonary hypertension and systemic hypotension that ensue in advanced heart failure (HF). RV end-diastolic pressure was significantly increased in HF. n=9 per group, *P<0.0001 vs time 0, Control (Ctrl). (C)Fractional area change of LV and (D)RV during the time course of cardiac pacing protocol; *P<0.05 vs Ctrl, analyzed by repeated measures ANOVA. (E)Sirius red staining of ventricular tissue. (F)Histological analysis indicated that collagen surface area was greater in failing RV than in failing LV. n= 5 per group. *P<0.01 vs respective Ctrl; #P<0.05 vs LV HF, analyzed by ANOVA on Ranks.