The goal of this observational study is to evaluating myocardial stiffness in patients with heart failure with preserved ejection fraction (HFpEF) by intrinsic wave velocity propagation (IVP). The main questions it aims to answer are:
* Whether myocardial stiffness assessed by IVP in patients with HFpEF Increased.
* Whether IVP is related to the cardiac structure and function in patients with HFpEF.
* What are the risk factors that may be associated with heart failure rehospitalization in patients with HFpEF?
* Whether increased myocardial stiffness is a risk factor for heart failure rehospitalization.
Participants will undergo transthoracic echocardiography to obtain conventional ultrasound parameters, and software post-processing analysis to obtained two-dimensional strain parameters and IVP, as well as general clinical data and laboratory test results. Clinical followed up was performed through electronic medical records or telephone interviews until patient rehospitalization for heart failure or discharge for one year.