Objective This study aimed to determine which parameters in transthoracic echocardiography (TTE) are more likely to be affected when applied in a critical care setting with mechanical ventilation.Methods Ninety mechanically ventilated ICU patients were enrolled into the study group. The control group consisted of 90 patients who underwent interventional therapy. All patients had bedside TTE for parametric measurements including the right ventricular size, septal kinetics and left ventricular ejection fraction (LVEF) by eyeballing (visual assessment), the tricuspid annular plane systolic excursion (TAPSE), mitral annular plane systolic excursion (MAPSE) by M-mode sonography, the right ventricular outflow tract velocity-time integral (RVOT VTI) and left ventricular outflow tract velocity-time integral (LVOT VTI) by pulse-Doppler, the right ventricular fraction of area change (FAC) and left ventricular ejection fraction (LVEF Simpson) by endocardium tracing. We compared the differences in the frequency of optimal image acquisition in assessments of these parameters between the two groups, as well as the differences in acquisition rates of parameter measurements in ventilated ICU patients. Results There were significantly fewer patients in the study group than in the control group who had optimal images acquisitions for parameter assessments with M-mode method, pulse Doppler method and endocardium-tracing method (P<0.05); no significant difference was obsered in the number of patients with optimal images for RV eyeballing and LVEF eyeballing between the two groups. In the study group, significantly fewer optimal images were acquired for FAC than for TAPSE (22.2％ vs. 72.2％, χ2=45.139, P<0.001) and RVOT VTI (22.2％vs. 71.1％, χ2=43.214, P<0.001); there were also fewer optimal images acquired for LVEF Simpson than for MAPSE (37.8％ vs. 84.4％, χ2=41.236, P<0.001) and LVOT VTI (37.8％ vs. 85.6％, χ2=43.455, P<0.001).Conclusions Images acquisition of optimal TTE images tend to be difficult in mechanically ventilated ICU patients, but eyeballing method for functional evaluation could be an alternative method. For quantitative parameters measurements, M-mode based longitudinal function evaluation and pulse Doppler-based VTI were superior to the endocardium-tracing based parameter assessments.