Cardiovascular comorbidities complicate interstitial lung disease (ILD) and represent potential therapeutic targets, yet the prevalence and clinical impact of left ventricular diastolic dysfunction (LVDD) remain poorly characterized. We aimed to evaluate LVDD as a potential treatable trait within a prospective cohort. Using data from an ILD registry (January 2021–October 2024), we defined clinically relevant LVDD as echocardiographic grade 2 or 3 diastolic dysfunction. Out of 276 patients (median age 69, 44% female), 14% had LVDD, which was almost entirely in patients with fibrosis (97%, p = 0.045) and associated with lower diffusing capacity for carbon monoxide. Survival and clinical analyses restricted to the fibrotic ILD subgroup (n = 241) showed that LVDD was independently associated with a higher hazard for a combined adverse outcome of acute exacerbation, lung transplantation, or death (adjusted HR 1.82, 95% CI 1.03–3.38, p = 0.043), which persisted after 1:2 propensity score matching (HR 2.04). LVDD also independently predicted increased all-cause mortality (adjusted HR 2.10) and reduced 6-min walk distance (median 413 vs. 465 m, β = −0.14, p = 0.036). In conclusion, LVDD is prevalent in fibrotic ILD and carries significant prognostic implications. Given its objective measurability and actionable treatment pathways, LVDD represents a potentially important treatable trait requiring multi-disciplinary care.