The objective of this prospective field study was to investigate whether commonly used criteria for clinical death occurred at the same time as cardiac death, as determined by electrocardiography. Specific ECG changes during euthanasia were also studied. Twenty-nine horses were euthanized with pentobarbital at two different dose rates and 15 of the 29 horses also received detomidine hydrochloride for sedation. ECG was recorded prior to and during euthanasia. Time to collapse, cessation of reflexes, heart sounds and asystole were recorded. ECG recordings were used to calculate RR intervals, PQ duration, QRS duration, distance from QRS complex to end of T wave corrected for HR (QTc interval), duration of T-wave from peak to end (TpeakTend) and amplitudes of T wave (Tpeak) before and during euthanasia. Differences between groups and ECG changes were evaluated using analysis of variance. Clinical determination of death occurred before cardiac death (P