The aims of the present study were to characterize ECG changes in calves with hyperkaliemia due to neonatal diarrhoea and to determine concomitant variations of serum concentrations of NO and of sonic cardiac markers such as cardiac troponins I and T and serum enzyme AST, LDH, CK and CK-MB activities. For that, ECG examinations were performed and serum biochemical parameters were measured in 13 diarrhoeic calves developing hyperkaliemia before and 5 hours after intravenous electrolyte (NaCl and Na(2)HCO(3)) administration and also in 5 healthy control calves. Compared to controls, diarrhoeic and hyperkaliemic calves exhibited significant alterations in electrolyte concentrations (Increases of K, Mg and P concentrations coupled to decreases of Na and Cl concentrations), a significant blood accumulation of nitrogen compounds (BUN and creatinine) and significant increases in ALP, LDH, CK and GGT activities. Furthermore, the serum NO concentrations have greatly enhanced in some individuals. By contrast, the serum troponin concentrations and the heart specific CK-MB and AST activities were similar between the 2 groups whereas electrocardiography changes were evidenced in diarrhoeic calves: P wave anomalies were observed in sonic diseased calves and the mean amplitude and the mean duration of the QRS complex and the T wave were markedly increased. The fluid electrolyte therapy has restored the electrolyte balance and has globally improved the parameters of the cardiac function but has failed to counteract the blood azote accumulation and the release of ALP, LDH, CK and GOT enzymes and even has aggravated the decreases in total protein and albumin concentrations and the glycaemia variations. These results suggest that the diarrhoea-related hyperkaliemia has led to disturbances into the cardiac function without inducing severe myocardium lesions in calves but was coupled to acute renal failure.