Step 1: The question asks which induction agent preserves cardiovascular function.
Step 2: Etomidate is well known for cardiovascular stability. Its induction dose produces only a negligible rise in heart rate, little fall in blood pressure or cardiac output, and minimal effect on coronary perfusion while reducing myocardial oxygen consumption.
Step 3: Propofol and thiopentone both cause myocardial depression and hypotension. Ketamine raises heart rate and blood pressure indirectly via sympathetic stimulation, but it has direct myocardial depressant action that is unmasked in catecholamine-depleted patients.
Step 4: Because of this haemodynamic stability, etomidate is the non-cardiodepressive agent and is the correct answer, useful in haemodynamically unstable or cardiac patients.