Background and purpose. Physiotherapists have been increasingly interested in investigating physiotherapy clinical reasoning and decision making processes. Cardiorespiratory physiotherapy has received little attention within this increasing body of research. This study aimed to investigate characteristics and processes of cardiorespiratory physiotherapy decision making and to contribute to the broader understanding of physiotherapy reasoning and decision making. Methods Fourteen cardiorespiratory physiotherapists took part in the study. Qualitative research methods were used guided by a philosophical hermeneutic approach. Participants were observed undertaking their usual daily patient care activities, and were later interviewed about their decision making. In-depth, iterative hermeneutic strategies were used to interpret the texts created by these processes to identify the nature and processes of decision making. Results Clinical decision making in cardiorespiratory physiotherapy is focussed on making decisions about the nature of patient's problems, physiotherapeutic intervention and interaction, and evaluation of effectiveness of actions. Cardiorespiratory physiotherapy decisions varied in their difficulty according to the attributes of the decisions. The variable nature of decisions influenced the reasoning processes used. Clinical decision making involved complex reasoning processes that were cyclic, evolving and flexible in nature, with inter-dependence and inter-relation between the different foci of clinical decision making. Clinical decision making was also found to be a social and collaborative process. Conclusions This study contributes to the body of literature on physiotherapy reasoning and decision making by revealing details about the characteristics and processes of cardiorespiratory physiotherapy decision making. This research can be used to shape the education of beginning practitioners and provide practising physiotherapists with a bfor critical appraisal of their decision making.