Heartbeat and respiration of southern elephant seals (Mirounga leonina), Weddell seals (Leptonychotes weddellii) and Antarctic fur seals (Arctocephalus gazella) were monitored simultaneously using a visual and non-intrusive method, at King George Island, South Shetland Islands. All three species demonstrated sleep apnoea with reduced heart rate. In adult elephant seals, heartbeat fell 18% in apnoea; spells lasted up to nine min, usually ending in disturbance from conspecifics or human visitors. Slight human disturbance (notably slight noise) reduced time spent in apnoea from over 40% to 4%, significantly reducing the frequency of falling into apnoea and increasing mean heartbeat. Further disturbance resulted in head raising, aggression, scratching, rolling and movement away. The visual monitoring of heartbeat and respiration can be used with resting or slightly disturbed animals but not when major body movements occur.