Background: Cor pulmonale (CP) is defined as the structural and functional alternation of the right ventricle (RV) caused by primary disorders of the respiratory system. We aimed to differentiate acute CP complicated with pulmonary thromboembolism (PTE) from chronic form due to chronic obstructive pulmonary disease (COPD) with strain analysis of RV. Patients and methods: From March 2005 to July 2006, total 52 patients, 24 consecutive patients with acute CP (10 males, mean 69짹10 years) and 28 consecutive patients with chronic CP associated with severe COPD (22 males, mean 63짹14 years), were included. Echocardiographic data and strain analyses were obtained with GE Vivid 7. Results: There was no statistical difference in age, fractional area change of RV, TR Vmax, and Tei index in both groups. However, males were more included in the chronic group. Midventricular systolic strain of RV was significantly decreased in patients with acute CP. Regarding the midventricular systolic strain in the detection of acute CP by the receiver operating curve, the best sensitivity and specificity were obtained when -12.2% was applied as the criterion (less than -12.6% for predicting an acute CP, the sensitivity, specificity and accuracy were 83.3%, 78.6% and 80.8%, respectively). Conclusions: Midventricular systolic strain of RV can be used in the differentiation between acute and chronic cor pulmonales.