Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality worldwide, with heart failure (HF) representing a major contributor to hospitalizations, healthcare costs, and death. Effective management of HF is hindered by the limitations of current biomarkers and diagnostic tools. Conventional biomarkers, such as natriuretic peptides, primarily reflect downstream hemodynamic stress and often lack specificity, particularly in HF with preserved ejection fraction or multiple comorbidities. While imaging provides valuable structural and functional information, it is resource-intensive, costly, and unsuitable for frequent longitudinal monitoring. As a result, these conventional approaches are inadequate to capture the dynamic and heterogeneous nature of HF pathophysiology. Circulating cell-free nucleic acids (cfNAs), including cell-free DNA (cfDNA) and RNA (cfRNA), have emerged as promising noninvasive liquid biopsy biomarkers capable of providing real-time insight into upstream pathological events, such as cardiomyocyte injury, immune activation, inflammation, and maladaptive remodeling. Importantly, cfNAs also act as active mediators of CVD pathology. When released under stress or injury, cfNAs interact with pattern recognition receptors (PRRs) that trigger sterile inflammation, cardiovascular cell dysfunction, and adverse cardiac remodeling. This review summarizes the origins, mechanistic roles, and clinical significance of cfNAs in HF and related CVD, highlighting their dual roles as diagnostic biomarkers and mechanistic effectors of disease. Finally, we discuss emerging cfNA-targeted therapeutic strategies, challenges, and future opportunities for precision medicine in HF and HF-associated CVD.