As right heart function can affect outcome in the critically ill patient, a thorough understanding of factors determining right heart performance in health and disease is pivotal for the critical care physician. This review focuses on fluid therapy, which remains controversial in the setting of impending or overt right heart failure. In this context, we will attempt to elucidate which patients are likely to benefit from fluid administration and for which patients fluid therapy would likely be harmful. Following a general discussion of right heart function and failure, we specifically focus on important causes of right heart failure in the critically ill, i.e. sepsis induced myocardial dysfunction, the acute respiratory distress syndrome, acute pulmonary embolism and the effects of positive pressure ventilation. It is argued that fluid therapy should always be cautiously administered with the right heart in mind, which calls for close multimodal monitoring.