High temperature and hyperkalemia cause exit block of action potentials at the atrioventricular junction of rainbow trout (Oncorhynchus mykiss) heart.

At critically high temperatures, atrioventricular (AV) block causes ventricular bradycardia and collapse of cardiac output in fish. Here, the possible role of the AV canal in high temperature-induced heart failure was examined. To this end, optical mapping was used to measure action potential (AP) conduction in isolated AV junction preparations of the rainbow trout (Oncorhynchus mykiss) heart during acute warming/cooling in the presence of 4 or 8 mM external K concentration.