To compare physical activity levels of patients in the first week after myocardial infarction (MI) and stroke.We conducted an observational study using behavioural mapping. MI patients were consecutively recruited from Alfred Hospital, Melbourne. Data for stroke patients (Royal Perth Hospital or Austin Hospital, Melbourne) were retrieved from an existing database. Patients were observed for 1 min every 10 min from 8 am to 5 pm. At each observation, the patient's highest level of physical activity, location and people present were recorded. Details of physiotherapy and occupational therapy sessions were recorded by the therapists.Proportion of the day spent physically inactive was lower in MI (n = 32, median 48%) than stroke (n = 125, median 59%) patients, but this difference was not significant in univariate or multivariate (adjusting for age, walking ability and days post-event) regression. Time spent physically active was higher in MI (median 23%) than stroke (median 10%) patients (p = 0.009), but this difference did not survive multivariate adjustment (p = 0.67). More stroke patients (78%) than MI patients (19%) participated in therapy.This study provides the first objective data on physical activity levels of acute MI patients. While they were more active than acute stroke patients, the difference was largely attributable to walking ability. Implications for rehabilitation In the first week after myocardial infarction, patients spent about half the day physically inactive (even though 81% were able to walk independently). Similar levels of inactivity were seen in a comparable cohort of acute stroke patients, suggesting that environmental factors play an important role. There appears to be wide scope for increasing levels of physical rehabilitation after acute cardiovascular events, though optimal timing and dose remain unclear.