The mature heart may be thought of as consisting of three layers, endocardium, myocardium, and an outer investing tissue called the epicardium. During early formation of the tubular heart of chick embryos, at about the 8-somite stage, two tissue layers become clearly discernible with the light microscope: the endocardium and the developing myocardial wall. The outer epicardial layer does not ap...

The epicardium is a critical tissue that directs several aspects of heart development, particularly via the secretion of soluble factors. This review summarizes recent approaches that implicate the epicardium as the source of mitogenic factors promoting cardiomyocyte proliferation, as the source of instructive signals that direct compact zone organization (morphogenesis), and as the tissue that...

Background. Prolonged membrane depolarization induced by an electric shock in the heart may produce propagation block leading to repetitive beats. We studied prolonged depolarization and its role in repetitive beats in a thin epicardial layer of endocardially prefrozen arterially perfused rabbit heart. Methods and Results. A laser scanner recorded optical action potentials at 63 sites within a ...

Introduction Temporary epicardial pacing is commonly used for rhythmic support in the acute postoperative period after cardiac surgery. Clinical studies suggest that pacing in the left ventricular epicardium during resynchronization therapy may be proarrhythmic in a minority of patients. The epicardial pacing increases transmural heterogeneity of repolarization. This could prolong the QT and JT...

A prolongation of the ventricular effective refractory period in response to cholinergic agonists or vagal stimulation has been demonstrated in a number of in vivo animal models. However, exposure of isolated myocardial tissues obtained from these hearts to as much as 10(-4) M acetylcholine has been shown to produce essentially no change in action potential duration or effective refractory peri...

Stimulation of coronary artery a receptors may decrease regional myocardial blood flow in patients with coronary artery disease. We studied 13 closed-chest conscious pigs to compare the role of vasoconstriction of coronary conductance vessels and that of arteriolar resistance vessels in this response. An artificial stenosis 7.5 mm long that caused an 82% reduction in vessel diameter was placed ...