Introduction. Patients with Heart Failure (HF) and preserved ejection fraction (HFpEF) show high mortality, yet not all its causes are fully understood. The aim of this study was to assess the hemodynamic response in HFpEF patients to an acute dose of sublingual nitro-glycerine (SL-NTG) during chronic vasodilator therapy. Methods. Colour M-mode Doppler (CMM) is a non-invasive ultrasound technique used to obtain left ventricular (LV) blood flow velocities during early filling and to calculate intra ventricular pressure gradients (IVPG). CMM recordings of 20 patients (HFpEF) during pre and post SL-NTG were obtained and processed with a specific algorithm to extract an IVPG map and related parameters. Average values from the available files were calculated and a Wilconox test was performed to compare the values during pre and post therapy, assuming a difference of p<0.05 as significant and of p<0.001 as highly significant. Results. The most relevant parameters identified as significantly different for pre and post treatment were reversal (p=0.03) and late (p=0.03) diastolic IVPG, E-wave velocity (p=0.003) and heart rate (HR)(p=0.02). Conclusion. Results are in accordance to the expecting effects for an acute SL-NTG dose: an increase in HR and myocardial contractility (late diastolic IVPG is directly related to atrial contraction) and a decrease in peak E-wave velocity, supporting the possible use of CMM technique as a follow up tool in the research of a more effective therapy for the HFpEF pathology.