An anonymous patient perception comprehension and satisfaction questionnaire was sent to 438 patients 1–3 months after they had participated in a clinical cardiovascular trial to examine the level of patient comprehension as perceived by the patient. We compared perceived comprehension in acute (acute myocardial infarction) and chronic (outpatient heart failure) clinical trials. Partially or fully completed questionnaires were received from 220 patients (70 chronic, 150 acute). The findings were similar in the 2 patient groups. Perceived full comprehension (understood most or all) of the trial was reported by 18 (27%) of chronic and 40 (31%) of 129 acute patients, while almost 20% of both groups reported little or no understanding of the trial. The level of comprehension was related to the recollected duration of explanation (p = 0.003 chronic, p < 0.001 acute). Perceived comprehension was not related to the personnel explaining the study (physician or nurse) or to whether the explanation as recollected was oral or written. However, in both acute and chronic patients, the majority (51% chronic; 63% acute) preferentially recalled the oral rather than written explanation of the trial. The very similar findings in the acute and chronic situation suggest that perceived understanding reflects human nature and willingness to be involved in medical issues. Considerable effort should be directed to improve the duration of explanation (particularly oral), if we are to achieve our goal of true informed consent in clinical cardiovascular trials.