Background: The aim of this work was to evaluate the effect of high intensity, interval exercise on echocardiographic markers of systolic and diastolic ventricular function among chronic heart failure (CHF) patients. Methods: A phase III clinical trial. Of the 100 consecutive CHF patients (NYHA class II-IV, ejection fraction<30%) that were randomly allocated to exercise treatment (n=50) or control (n=50), 72 (exercise group, n=33, 63±9 years, 88% men, 70% ischemic heart failure and exercise group, n=39, 56±11 years, 82% men, 70% ischemic heart failure) completed the study. Particularly, the intervention group followed a high intensity, interval ergometric aerobic training (i.e., 30 sec at 100% of max workload, 30 sec at rest) for 30 min/day-by-12 weeks, whereas the control group received regular instructions. Echocardiographic assessment was performed in all patients before and after the intervention. The pulsed tissue Doppler imaging (TDI) of mitral annulus was characterized by the systolic wave Smv, and the diastolic waves: Emv and Amv. Furthermore the ratio E/Emv and the flow propagation velocity, left ventricular outflow velocity integral (VTI), and left atrial fraction were calculated; where E is the rapid mitral filling wave. The bioethics committee approved the protocol. Results: Both groups reported similar physical activity status at baseline, as assessed through the IPAQ (p=0.60), had similar body mass index (p=0.08), smoking habits (p=0.17), hypertension (p=0.15), diabetes (p=0.46) and dyslipidemia (p=0.83). General mixed effects models revealed that intervention group increased VTI by 4% (p=0.05) as compared with the control group in which no significant change was observed (p=0.47).Furthermore, the intervention group decreased Emv/Vp by 14% reduction (p=0.06), decreased E to A ratio by 24% (p=0.004) and decreased by 8% E to Emv ratio (p=0.05), with no significant change on control group (all p>0.05). Additionally, intervention group improved 6-minutes-walk test by 13% as compared with intervention group (p=0.10), the VO2 max level by 12.5% ml/kg/min (p=0.002), the VCO2 level by 21% L/min (p=0.01), and total power by 83% watts (p=0.04), as compared with the intervention group. No significant differences were detected in both groups according to left ventricular ejection fraction, but a modest reduction of pulmonary artery systolic pressure, left atrial fraction in the intervention group. Conclusion: High intensity, systematic aerobic training seems to improve left ventricular diastolic function in parallel with an improvement in ergometric capacity and tissue oxygen delivery.