OBJECTIVE It has been reported that breathing exercise by immersion in combination with expiring into water improved pulmonary function and blood-gas exchange in patients with chronic obstructive pulmonary disease (COPD). This effect may result from respiratory muscle exercise against hydraulic pressure and decreased dead space by increased sub-abdominal pressure. Increased cardiac function by bathing is suggested to contribute to the effect. To clarify the effect of the breathing exercise by immersion on cardiac function, a study was made of cardiac function during the exercise in patients with emphysema. METHODS Echocardiography, respiratory function test and arterial blood gas analysis were performed during a two-month breathing exercise programme in a pool filled with 38 degrees C water for 12 patients (aged 70.9 +/- 9.1 years) with stable chronic pulmonary emphysema who were treated at our hospital between 1993 and 1996. The patients breathed in whilst standing in a pool and breathed out through the mouth while sinking the nose under water. This exercise was repeated for 30 min per day and continued for six days a week for two months. RESULTS The ejection fraction increased significantly after each 30-minute exercise (N = 12; p < 0.01) as well as after the two-month exercise programme (N = 12, p < 0.05). Left ventricular end-diastolic and systolic dimensions at rest decreased significantly after the two-month exercise programme (N = 12, p < 0.01). The ratio of forced expired volume in one second to forced vital capacity (FEV1:FVC) increased and PaCO2 decreased following this programme (N = 12, p < 0.05). CONCLUSIONS These results suggest that the breathing exercise by immersion is useful not only in treating emphysema but also in improving cardiac function.