Background: We investigated preoperative physical activity (PA) and sedentary behaviour (SB) in patients scheduled for elective cardiac procedures and compared them with population-based sample of Finnish adults. Methods: Cardiac patients (n = 139) undergoing cardiac operations carried a triaxial accelerometer for seven days during the month before the procedure. Patients were categorised into four groups according to the procedure: percutaneous coronary intervention or coronary angiography (PCI-CA), coronary artery bypass grafting (CABG), aortic valve replacement (AVR) and mitral valve surgery (MVS). The raw accelerometer data was analyzed with dedicated algorithms to determine metabolic equivalents (METs, 3.5 mL/kg/min of oxygen consumption) of PA. The intensity of PA was divided into two categories: light (LPA, 1.5–2.9 METs) and moderate-to-vigorous (MVPA, ≥ 3.0 METs), while SB represented intensity < 1.5 MET without movements. SB and PA were described as daily means and accumulation from different bout lengths. Daily standing, steps and mean and peak MET-values were calculated. The results were compared between the patient groups and against the reference group from a population-based study FinFit2017. Results: Cardiac patients had fewer daily steps than the FinFit population (p = 0.01), and less SB accumulating from < 20 min bouts (p = 0.002) but more from 20 to 60 min bouts (p = 0.002). Particularly, CABG group had less daily MVPA (p = 0.002) and MVPA accumulating from > 10 min bouts (p < 0.001) than the FinFit population. Conclusions: We found large differences in PA and SB between the patient groups and the FitFit population, CABG group having the worst activity profile. Also, the variation within the patient groups was wide, which should be considered to individualise the rehabilitation programs postoperatively. Trial registration clinicaltrials.gov (NCT03470246). Registered 19 March 2018, https://clinicaltrials.gov/ct2/show/NCT03470246.