Aims: We documented the midterm prognosis of left ventricular thrombus (LVT) in heart failure (HF) patients with dilated cardiomyopathy (DCM) and ischaemic cardiomyopathy (ICM). We aimed to characterize patients with LVT in the context of HF with reduced (≤40%) left ventricular ejection fraction and evaluate their risk for death and/or embolic events, overall, and specifically in patients with ischaemic or non-ischaemic aetiology. We also intended to identify risk factors for LVT in patients with DCM. Methods and results: We included all HF patients (N = 105, age 56 ± 13) admitted from 2005 to 2018 in our institution for LVT without significant valve disease/prosthesis, heart transplant/left ventricular assist device, congenital heart disease, or acute myocardial infarction. Our primary endpoint was the 1 year risk of the composite of all-cause mortality (ACM) and symptomatic embolic events. Mean left ventricular ejection fraction was 23 ± 9%, and median BNP was 1795 pg/mL. Most (97%) patients were treated with vitamin K anticoagulants, and 64% had ICM. Symptomatic embolic events and/or ACM occurred in 20% of the population [embolic events (all within 30 days of LVT diagnosis) 15% and ACM 6%] and was similarly frequent in DCM or ICM (P > 0.05). Suspected/transient embolic events were more frequent in DCM (overall 13%; 29% in DCM vs. 5% in ICM, P < 0.01). Major bleeding occurred in 5% of patients. Left ventricular reverse remodelling occurred in 65% of patients, more frequently in DCM (86% in DCM vs. 65% in ICM, P = 0.02). In a case-control analysis matching DCM patients, BNP level was the only factor significantly associated with LVT (2447 pg/mL in LVT vs. 347 pg/mL, P < 0.001). Conclusions: Patients with LVT have markedly high natriuretic peptides and experience a 20% 1 year risk for embolic events and/or death following diagnosis despite anticoagulant treatment. Most patients have favourable remodelling/recovery. As all symptomatic embolic events occurred within 30 days of LVT diagnosis, a very careful initial management is warranted.