Does the ventricle limit cardiac contraction rate in the anoxic turtle ()? II. and assessment of the prevalence of cardiac arrythmia and atrioventricular block.

Previous studies have reported evidence of atrio-ventricular (AV) block in the oxygen-limited heart. However, if cardiac arrhythmia occurs in live turtles during prolonged anoxia exposure remains unknown. Here, we compare the effects of prolonged anoxic submergence and subsequent reoxygenation on cardiac electrical activity through electrocardiogram (ECG) recordings of 21 °C- and 5 °C-acclimated turtles to assess the prevalence of cardiac arrhythmia.

Indirect evidence that anoxia exposure and cold acclimation alter transarcolemmal Ca flux in the cardiac pacemaker, right atrium and ventricle of the red-eared slider turtle (Trachemys scripta).

We indirectly assessed if altered transarcolemmal Ca flux accompanies the decreased cardiac activity displayed by Trachemys scripta with anoxia exposure and cold acclimation. Turtles were first acclimated to 21 °C or 5 °C and held under normoxic (21N; 5N) or anoxic conditions (21A; 5A). We then compared the response of intrinsic heart rate (f) and maximal developed force of spontaneously contracting right atria (F), and maximal developed force of isometrically-contracting ventricular strips (F), to Ni (0.