Background and Objectives: Understanding worsening heart failure events (WHFEs) and clinical practices in the real world is essential in heart failure (HF) management. The primary objective of this single-center, retrospective, observational study, including a patient survey, was to characterize WHFEs and associated factors during the first year after the incident HF diagnosis in Finnish patients. Secondly, implementation and adherence to guideline-directed medical therapy (GDMT) and mortality during the whole follow-up were assessed. Methods: Incident HF patients (International Classification of Diseases, 10th Revision: I50) with reduced ejection fraction (HFrEF; <40%) were identified between 2013–2019 from the hospital data lake of Southwest Finland. Clinical characteristics, healthcare resource utilization, medication prescriptions and purchases, and deaths were collected from hospital records and national registers between 2011–2021. A survey was linked with register data for a subgroup of patients. Associations between explanatory factors, WHFEs, and mortality were studied using logistic and Cox regression models. Results: Among 570 HFrEF patients, 23% (n=133) experienced a WHFE within the first year after the incident diagnosis. During this 1-year period, 85% used angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, 90% beta-blockers, and 44% mineralocorticoid receptor antagonists, and >80% of patients were adherent to these medications. WHFEs were associated with higher risk of mortality (hazard ratio [HR], 1.82; 95% confidence interval [CI], 1.31–2.53; p<0.001), whereas adherence was associated with a lower risk of WHFEs (odds ratio, 0.31; 95% CI, 0.20–0.48; p<0.001) and mortality (HR, 0.66; 95% CI, 0.47–0.94; p=0.021) in multivariate models. Quality of life was lower in patients with (n=47) than without WHFEs (n=100). Conclusions Improving adherence is crucial for mitigating adverse outcomes in HF.