Abstract Body (Do not enter title and authors here): Background: Heart disease continues to be the leading cause of death in the United States in 2025. Ill-defined descriptions of heart disease may lead to misclassification of deaths by ICD codes, potentially obscuring the growing clinical burden and masking disparities among high-risk populations and regions across the U.S.

Research Question: What are the temporal trends in mortality due to complications and ill-defined heart disease from 1999 to 2020 in U.S?

Methods: We abstracted data from CDC-WONDER database using ICD-10 code: I51, from 1999-2020. Age-Adjusted Mortality Rate (AAMR) per 100,000 population and Annual Percentage Change (APC) along with 95% confidence intervals (CI) were determined. Joinpoint regression analysis (v 5.4.0.0) was used to examine trends stratified by overall, sex, race/ethnicity, age-group, states, census region and 2013 urbanization.

Results: A total of 863,974 deaths related to ill-defined descriptions of heart disease were reported between 1999-2020, with a steady increase in overall AAMR (11.80), and an APC of 1.56 (95% CI 1.29 to 1.82, p <0.000001). Males had overall higher AAMR (15.22) compared to females (8.94). Non-Hispanic (NH) Blacks or African American exhibited overall highest AAMR (16.49), followed by NH-American Indian or Alaska Native (12.49). People aged 85+ years outweighed all age-groups with a strikingly high overall AAMR (211.74). States in top 90^th percentile; Alabama (21.16), Louisiana (21.58), Georgia (23.29), Mississippi (29.99) had a roughly 4-5 times difference in the overall AAMR than states in the lower 10^th percentile; Massachusetts (6.43), Virginia (8.14), New York (8.15). By census region, the South had the overall highest AAMR (14.24) followed by Midwest (11.42). Similar disparities were noted in urban-rural status, with Non-metropolitan displaying overall highest AAMR (15.62).

Conclusions: The disproportionately high mortality rates among NH-Blacks or African American, NH-American Indians or Alaska natives and non-metropolitan regions of states in the South (Louisiana, Georgia, Mississippi) underscore the urgent need for improved diagnostic accuracy, standardized cause-of-death certification, and equitable access to quality healthcare. Addressing these gaps is essential for shaping informed and effective health policy across the United States.