Passive Predetermination of the Heart: A Cross-Domain Evidence Synthesis from Embryogenesis, Birth Transition, and Allometric Scaling

Cardiac physiology has accumulated a set of core observational facts—including the necessity of pulsation, sinoatrial node autonomous pacing, all-or-none action potential, topological differentiation of arteries and veins, the near-absence of cardiomyocyte division, heart failure with preserved ejection fraction, tachycardia-induced heart failure, age-dependent decline in maximum heart rate, and the irreversible progression of atrial fibrillation—that are currently dispersed across separate domains of electrophysiology, hemodynamics, and pathophysiology. This paper proposes that these facts can be coherently organized within a single physical framework: the heart is the dissipation center geometrically predetermined at the moment of energy injection in a multicellular aggregate. Three independent categories of publicly available data are synthesized to evaluate this proposal: (1) cross-species embryogenesis timelines in 16 vertebrate species, (2) clinical data of birth circulatory transition in humans and animal models, and (3) cross-species allometric scaling relationships. The embryogenesis data show that the timing of the first heartbeat converges on a narrow somite-stage range across species with gestation lengths differing by an order of magnitude, consistent with a diffusion-limit trigger, although the critical variable—embryo cross-sectional thickness at first heartbeat—has not been systematically measured in any species, representing an open empirical gap. The birth transition data reveal a strict temporal sequence in which physical pressure and oxygen partial-pressure changes precede and drive functional closure of the foramen ovale and ductus arteriosus, with no documented instances of reversed causality. The allometric scaling data, analyzed using phylogenetic generalized least squares regression across 214 mammalian species, demonstrate that body mass alone explains 94.7% of the variance in heart rate (Pagel's lambda = 0.89), while ecological variables contribute negligible independent explanatory power (delta AIC = 9.4 favoring the physical constraint model over the ecological adaptation model). The convergence of physical pointers from three independent domains provides a working framework for cardiac biophysics that generates specific, falsifiable predictions. All data are from publicly available published sources and can be independently verified.