Aqua exercise and swimming are traditionally recommended for low risk cardiac patients. In patients with severe myocardial infarction (MI) and compensated severe chronic heart failure (CHF), physicians may have reservations about water exercises and swimming. Concerns become understandable when central haemodynamic responses in healthy subjects during immersion and swimming are considered.

During neck deep water immersion, a 100 cm column of water exerts a pressure of 76 mm Hg on the body surface. During swimming, a pressure of 40–60 mm Hg can be assumed. This pressure compresses superficial veins, particularly of the lower extremities and abdomen, resulting in a blood volume shift to the thorax and heart. On immersion up to the iliac crest, the blood volume shift is not significant, but, on immersion up to the neck, the central blood volume has been shown to be increased by about 700 ml; 180–240 ml of this was allotted to the heart volume, with enlargement of all four chambers.¹ Planimetry of the diastolic poster-anterior area of the heart has shown an average increase in heart size of 30% within six seconds.² From a central haemodynamic point of view, crucial immersion starts at the diaphragm/xiphoid level. At this level, both the buoyancy effect³ and the external hydrostatic pressure result in a blood volume shift, which (a) corresponds to up to 85% of …