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Early mortality is a formidable challenge in the poultry industry, leading to substantial losses in profitability, health and welfare, efficiency, and sustainability. A large proportion of this mortality is caused by heart conditions, such as ascites syndrome, sudden death syndrome, pulmonary hypertension syndrome, and hypertrophic cardiomyopathy. The prevalence of these issues has been consistently increasing and has been hypothesized to be associated with strong selection pressure to increase meat yield, in particular breast meat. However, the relationship between meat yield and cardiovascular health is unclear across the published literature. Therefore, a systematic review and meta-analysis were conducted which identified 22 publications that met the inclusion criteria. Body weight (BW), portion yields (i.e., whole breast, fillet, tender, leg, drumstick, thigh, wing), organ weights (i.e., heart, lungs, liver), and incidence of ascites were extracted from the chosen studies to describe the relationship between portion and organ weights. A generalized linear mixed model treating study as a random effect was implemented in SAS 9.4 to examine the relation between breast meat and heart weight across studies. The model included heart weight (% BW) as the dependent variable as well as species (chicken vs. turkey), species purpose (egg vs. meat), ascites presence (yes vs. no), and the interaction between breast meat yield (% BW) and species. Species (P < 0.0001) and species purpose (P < 0.0001) were significantly associated with heart weight. On average, turkey and chicken heart weights were 1.16 ± 0.19 % and 1.01 ± 0.1 % BW, respectively. Birds selected for egg production (1.41 ± 0.177 % BW) had heavier hearts than birds selected meat production (0.76 ± 0.110 % BW). There was also a significant interaction between species and breast meat yield (P < 0.0001). In turkeys, heart weight decreased by 0.02 ± 0.0006 % BW for every 1% increase in breast meat yield, whereas in chickens heart weight increased by 0.04 ± 0.007% BW for every 1% increase in breast meat yield. The presence of ascites was not associated with heart weight (P = 0.1202). These findings demonstrate that birds selected for meat production have smaller hearts (% of BW) compared with those selected for egg production which provides support for the hypothesis that intense selection for meat yield is affecting the cardiovascular system in poultry. Interestingly, the relationship between breast meat yield and heart weight is not the same for chickens and turkeys. Further work is ongoing to consider other carcass portion variables in the meta-analysis as well as investigate if differences in heart size are related to the aforementioned heart conditions. Overall, this study illuminates areas of further research as the poultry industry works to improve health and welfare, while maintaining production to meet global demand for poultry products. [ABSTRACT FROM AUTHOR]