Increased myocardial trabeculations define noncompaction cardiomyopathy (NCC). Imaging advancements have led to increasingly common identification of prominent trabeculations with unknown implications. We quantified and determined the impact of trabeculations' burden on cardiac function and stretch in a population of healthy young adults. One hundred adults aged 18 to 35 years (28±4 years, 55% women) without known cardiovascular disease were prospectively studied by cardiovascular magnetic resonance. Left ventricular (LV) volumes, segmental function, and ejection fraction (EF) and left atrial volumes were determined. Thickness and area of trabeculated (T) and dense (D) myocardium were measured for each standardized LV segment. N-terminal pro-brain natriuretic peptide (Nt-pro-BNP) was measured. Eighteen percent of the subjects had ≥1 positive traditional criteria for NCC, and 11% meet new proposed NCC cardiovascular magnetic resonance criteria. Trabeculated over dense myocardium ratio (T/D) ratios were uniformly greater at end-diastole versus end-systole (0.90±0.25 vs 0.42±0.13, p<0.0001), in women versus men (0.85±0.24 vs 0.72±0.19, p=0.006), at anterior versus nonanterior segments (1.41±0.59 vs 0.88±0.35, p<0.0001), and at apical versus nonapical segments (1.31±0.56 vs 0.87±0.38, p<0.0001). The largest T/D ratios were associated with lower LVEF (57.0±5.3 vs 62±5.5, p=0.0001) and greater Nt-pro-BNP (203±98 vs 155±103, p=0.04). Multivariable regression identified greater end-systolic T/D ratios as the strongest independent predictor of lower LVEF, beyond age and gender, left atrial or LV volumes, and Nt-pro-BNP (β=-9.9, 95% CI -15 to 4.9, p<0.001). In conclusion, healthy adults possess variable amounts of trabeculations that regularly meet criteria for NCC. Greater trabeculations are associated with decreased LV function. Apparently healthy young adults with increased trabecular burden possess evidence of mildly impaired cardiac function.