In humans, the lateral recumbent position has a beneficial effect on haemodynamics. If this effect is substantial in small animals too, there is a risk of misinterpretation in preclinical investigations. Therefore, the aim of this study was to analyse the impact of acute changes in body position on haemodynamics in rats. Healthy rats (n = 21) and rats post myocardial infarction (n = 20) were randomly positioned supine, prone, or on the right or left side. In each position, we measured haemodynamic parameters by pressure-tip catheter and thermodilution. We found that left ventricular contractility (dP/dt max ) was significantly elevated in both lateral positions as compared to the supine position in healthy rats. In healthy rats and following infarction, cardiac index (CI) and stroke volume index (SVI) were significantly higher in both lateral positions as compared to the supine or prone position. Of importance, if SVI values in the supine position in healthy rats (0.095 ± 0.003 ml (100 g) −1 ) are compared to SVI values measured in different positions after myocardial infarction, the SVI can be either significantly lower in the supine (0.084 ± 0.003 ml (100 g) −1 ) or significantly higher in the left lateral position (0.105 ± 0.003 ml (100 g) −1 ). We conclude that post myocardial infarction and in healthy control rats, important haemodynamic values are increased in lateral positions as compared to prone or supine positions. Analysing haemodynamic data in rats may therefore result in misinterpretation if the body position is inconsistent.