INTRODUCTION: The epidemic of pneumonia caused by a new coronavirus disease 2019 (COVID-19) rapidly spread all over the world. Pathophisyology of the cardiovascular effects of COVID-19 is still not well known. Myocardial dysfunction may occur in cytokine-based immune reactions. Myocardial performance index (MPI) is a feasible parameter that reflects systolic and diastolic cardiac functions. We aimed to evaluate the MPI in patients with COVID-19. METHODS: The study consisted of 40 patients diagnosed with COVID-19 who had mild pneumonia and did not need intensive care treatment. All patients underwent echocardiographic evaluation. The MPI and laboratory parameters were compared between the acute period of infection and after clinical recovery in patients with COVID-19. RESULTS: Statistically significant higher MPI (0.56±0.09 versus 0.44±0.07, p<0.001), longer isovolumic relaxation time (112.3 ±13.4 versus 91.8±12.1ms, p<0.001), longer deceleration time (182.1 ± 30.6 versus 161.5 ± 43.5ms, p=0.003), shorter ejection time (279.6±20.3 versus 298.8±36.8ms, p<0.001) and higher E/A ratio (1.53±0.7 versus 1.22±0.4, p<0.001), were observed during acute period of infection compared to ones after clinical recovery. Compared with basal values, no significant change in left ventricular (LV) systolic ejection fraction was observed after clinical recovery (60.3 ± 3.2% versus 61.7±2.4%, p>0.05). CONCLUSION: Our study showed that although, LV systolic function appear normal in COVID-19 patients, they have globally reversible LV diastolic dysfunction, based on tissue Doppler derived MPI. This could be due to isolated subclinical diastolic dysfunction. The underlying mechanism and its clinical significance can be established by further studies.