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Behavioral factors and cardiovascular changes associated with myocardial degeneration and cardiac arrest induced by shock avoidance stress were studied. Pairs of avoidance and yoked squirrel monkeys were exposed to a 24‐hr session. Myocardial degeneration and cardiac arrest were more readily induced in avoidance than yoked monkeys. The cardiac lesions were not related to body weight, aggressive behavior, or number of shocks received during stress, but an increased heart rate without hypertension during the first stress hour was more evident in avoidance than yoked monkeys. These cardiac changes were attributed to an autonomic disturbance associated with the response contingencies of the avoidance situation. An autonomic effect also appeared to be involved with stress‐induced death. These deaths were characterized by a sudden, severe bradycardia without initial hypotension and cardiac arrest which was attributed to either parasympathetic activation or sympathetic inhibition. While heart rate decreased in all monkeys, stress‐induced death followed only in monkeys which gave up and stopped contending with the stress. Thus, stress‐induced myocardial changes and death were related to autonomic disturbances precipitated by psychological stress.

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Background South Asians have a low prevalence of atrial fibrillation (AF) in comparison with White Europeans despite a higher burden of hypertension, diabetes mellitus and coronary artery disease. The reason for this disparity is unclear but may relate to electrophysiological or structural differences within the atria or variations in autonomic function. We aimed to assess these areas using a range of non-invasive cardiac investigations. Methods A prospective cohort study was performed on 200 South Asian and 200 Caucasian healthy volunteers aged 18–40 years. All subjects underwent electrocardiography (ECG), echocardiography and anthropometric measurements. Eighty subjects in each cohort underwent 24 hour ambulatory ECG and fifty subjects in each cohort underwent exercise testing. Results Compared with White Europeans, South Asians were of a smaller height with lower lean body mass and smaller left atrial size. They had reduced P wave dispersion and P wave terminal force in lead V 1 . South Asians had a lower burden of supraventricular ectopy. They had a higher mean heart rate and South Asian males had lower heart rate variability, suggestive of sympathetic predominance. Exercise capacity was lower in South Asians. Conclusions South Asians have differences in left atrial size, P wave indices, burden of supraventricular ectopy, heart rate, heart rate variability and anthropometric measurements. These differences may relate to variations in atrial morphology, atrial electrophysiology and autonomic function and might help to explain why South Asians are less susceptible to developing AF.