Effects of Heparin on the Electrophysiological and Mechanical Properties of Early Embryonic Chick Hearts

The effect of heparin (1–200μg/ml) on several functional properties of 4-day-old embryonic hearts was studied. Intracellular recordings either from cells of the atrium, the atrio–ventricular canal or the ventricle were made on the isolated and perfused hearts. In all impaled myocardial cells, heparin produced an increment in the maximal rate of rise and amplitude of the action potentials and the duration was slightly diminished. In addition, heparin provoked a reduction in the spontaneous beating frequency, while the electrical excitability and the conduction velocity of the atrium and the ventricle were increased. The measurements of atrio–ventricular latency revealed that it was diminished, i.e. the propagation of impulses through the atrio–ventricular canal was improved. Simultaneously with these changes, heparin incremented the amplitude of contraction of either the atrium or the ventricle importantly.