Background: In patients undergoing elective cardiac surgery, the prevalence of inspiratory muscle weakness is not well-understood. This information could guide pre-operative therapy. Objectives: To determine the prevalence of inspiratory muscle weakness in preoperative cardiac surgery patients, and describe relationships between pre-operative factors (including maximal inspiratory pressure, MIP) and post-operative pulmonary complications (PPCs). Methods: Prospective study of elective cardiac surgery patients. Pre-operative MIP was measured (cmH2O) and PPC data were extracted from medical records (Melbourne Group Score) while age, height, weight, frailty and physical activity levels were captured via questionnaire. Backwards-stepwise logistic regression was used to describe associations. Results: 24 participants were recruited (79% male, age 70 ± 10.7, BMI 26.8 ± 4.14). The prevalence of inspiratory muscle weakness (MIP < 60% predicted) was 25% (n = 6). PPCs were associated with body mass index (BMI) (r = 0.464, p = 0.022). Conclusion: The prevalence of pre-operative inspiratory muscle weakness was 25%. BMI may be an important determinant of PPCs in elective cardiac surgery patients.