Objectives: Small ventricular septal defects (VSDs) are considered to have great prognoses and most remain unrepaired. However, we have recently demonstrated lower functional capacity in patients with small VSDs compared with healthy peers. Using magnetic resonance imaging scans, we determined whether the functional capacity was correlated to the size of the shunt.

Methods: We included patients with unrepaired VSDs and healthy adults between 18 and 40 years of age in a prospective, cohort study. Functional capacity was previously determined using an incremental bicycle test, establishing peak oxygen uptake. Magnetic resonance imaging scans were performed using a 1.5-tesla Philips scanner. With electrocardiographically triggered flow measurements, we calculated mean cardiac output from the pulmonary trunk and ascending aorta as well as vessel diameters.

Results: In total, 29 patients with unrepaired VSDs (26.5 ± 6 years) and 25 controls (26.9 ± 5 years) completed both studies. Previously measured peak oxygen uptake was nearly 20% lower in patients compared with controls (P = 0.002). All patients had shunt ratios below 1.5, with mean QpQs of 1.2 ± 0.1. When correlating shunt size to functional capacity, a negative correlation was found between the shunt ratio and peak oxygen uptake (r  = −0.44, P = 0.020). Compared with controls, patients had increased forward and retrograde flow in the pulmonary trunk but comparable flows in the ascending aorta. Pulmonary diameter was also increased in patients (30.3 ± 4 mm) compared with controls (28.2 ± 3 mm; P = 0.041), whereas aortic dimensions were comparable.

Conclusions: Our results demonstrate that, although small, unrepaired VSDs revealed reduced functional capacity that can be negatively correlated to the size of the shunt.