During a 20-month period a "cardiac" ambulance was manned on alternate days by specially-trained ambulance personnel only, or by such personnel plus a doctor. The presence of a doctor did not lead to any reduction in the mortality of patients with heart-attacks. Although transport to hospital by the special service was associated with a low pre-hospital mortality, this was balanced by a high pre-hospital mortality in the group of patients brought to hospital by routine ambulances at times when the special vehicle was manned, but for some reason was not used. There was evidence of unintentional selection of low-risk cases for transport by the cardiac ambulance. The number of lives saved by the special service was too small to cause any significant reduction in the overall mortality from heart-attacks in Nottingham.