Abstract: Embryo heart rates were measured on 400 fertilized turkey eggs (399 viable embryos) at 4 day intervals beginning at day 12 of development. Heart rates varied directly with eggshell porosity and were significantly and positively correlated with eggshell conductance (G) and conductance constants (k) but not with initial egg weight. When only eggs with embryos that died were analyzed the significant correlation coefficients increased. In a second experiment, eggshell pores were occluded to reduce G then heart rates were measured. Heart rates decreased concomitantly with decreases in G. In the final experiment, approximately 15,912 eggs were weighed individually to calculate G for each egg and were then incubated. Embryo survival was noted in High and Low G groups. Embryo heart rate and cardiac physiology in each group was measured. Low G reduced heart rates and improved embryo survival and cardiac physiology compared to High G. Thus, cardiomyopathy due to High G and its consequent lack of energy for myocardial function may contribute to turkey embryo mortality late in development.