There is a significant interrelationship between cardiovascular disease and obstructive sleep apnea (OSA), as they share common risk factors and comorbidities. This study aimed to investigate the knowledge, attitude, and practice (KAP) of inpatients with cardiovascular disease towards OSA. This cross-sectional study was conducted between January, 2022 and January, 2023 at Zhongda Hospital Affiliated to Southeast University among inpatients with cardiovascular disease using a self-administered questionnaire. A self-designed questionnaire was used to assess KAP, and the STOP-Bang questionnaire was applied to evaluate participants' OSA risk. Spearman correlation and path analyses were conducted to explore relationships among KAP scores and high OSA risk. Subgroup analyses were conducted within the high-risk population identified by the STOP-Bang questionnaire. In a study analyzing 591 questionnaires, 66.33% were males. Mean scores were 6.81 ± 4.903 for knowledge, 26.84 ± 4.273 for attitude, and 14.46 ± 2.445 for practice. Path analysis revealed high risk of OSA positively impacting knowledge (β = 2.351, P < 0.001) and practice (β = 0.598, P < 0.001) towards OSA. Knowledge directly affected attitude (β = 0.544) and practice (β = 0.139), while attitude influenced practice (β = 0.266). Among high OSA risk individuals, knowledge directly impacted attitude (β = 0.645) and practice (β = 0.133). Knowledge indirectly influenced practice via attitude (β = 0.197). Additionally, attitude directly affected practice (β = 0.305). These findings provide insights into the interplay between OSA risk, knowledge, attitude, and practice. Inpatients with cardiovascular disease demonstrated inadequate knowledge, moderate attitude, and practice towards OSA. The findings highlighting the need for targeted educational interventions to improve awareness and management of OSA.