Early ventricular filling is influenced by active relaxation and left atrial pressure. Abnormalities of early filling are especially important in complex congenital heart disease palliated by modified Fontan procedures. To date, the normal values and effects of different haemodynamic loads on active relaxation have not been assessed in children. This study therefore measured the time constant of relaxation (τ) in children with the following conditions. There were 7 normal (Gp.1)(mean age 10.1y); 12 aortic stenosis and 8 coarctation (pressure load), (Gp.2)(9.3y); 8 aortic regurgitation (volume load)(Gp.3)(10.1y); 4 cardiomyopathy (Gp.4)(11.5y); 8 univentricular hearts(Gp.5)(5.5y).

At cardiac catheterization, τ was calculated from -1/slope of hi-fi LV pressure decay measured from peak -dp/dt. The groups were compared by anova, and unpaired t-test with Bonferroni correction and regression was performed.

Mean τ for Gp.1=29.7, Gp.2=28.1, Gp.3=34.8, Gp.4=36.1, Gp.5=34. Gp.2 vs Gp.3, (p=0.007). Correlation of τ with indices of systolic and diastolic function were: Ejection fraction, R=-0.5305, p=0.0001. Peak systolic volume, R=0.5489, p=0.0001. End-diastolic volume, R=0.5306, p=0.0001. Wall mass, R=0.4705, p=0.001. -dp/dt, R=-0.4686, p=0.0007. +dp/dt, R=-0.5116, p=0.0007. Ratio of stress at end-systole/end-systolic volume, R=-0.5773, p< < 0.001.

This data confirms the load interdependence of active relaxation, ie. shortening of τ with pressure load and increased contractility while lengthening of τ occurs with volume loading and cardiomyopathy. These may influence early filling and therefore overall cardiac function in pre and post-operative congenital cardiac malformations. Treatment may be directed to improve filling.