&NA;We examined the longitudinal propagation of contraction in isolated human and pig coronary arteries. Epicardial coronary arteries of about 2 cm were cut open longitudinally, and the tension development of circular muscles was measured simultaneously at three sites (both cut ends and the midportion of the segment). Cyclic tension changes arising at one site of human coronary artery propagated smoothly to the other sites, and the whole length of segment worked as a single unit. Contraction induced by locally applied prostaglandin F2&agr;or histamine also propagated in four of seven preparations. The remaining three human and all seven pig coronary arteries showed propagation of such drug‐induced contraction after treatment with 10 mM tetraethylammonium (TEA). In pig coronary arteries treated with TEA, electrical stimulation evoked a reproducible local contraction and its propagation. Propagation velocity was 9.0±0.7 at 0.8 mM calcium concentration and increased to 11.1±0.9 and 13.1±1.4 mm/sec as calcium concentration rose to 1.8 mM and 7.2 mM, respectively. Local contraction did not propagate at calcium concentrations of 0.2 mM or less. The calcium antagonist diltiazem decreased the propagation velocity dose dependently and blocked propagation of contraction at 0.3 &mgr;M without significant effects on the magnitude of local contraction. We conclude that smooth propagation of contraction develops in epicardial coronary arteries of humans and pigs and that the propagation may depend on calcium influx. (Circulation Research1989;64:734‐741)