Although many events in clinical pediatric cardiology require the evaluation of the pathophysiology of heart failure, accurate measurement and evaluation of diastolic function, which is an important aspect of hemodynamics, remain difficult. Ventricular diastolic function can be classified into early diastolic relaxation and late diastolic stiffness. Early ventricular diastolic relaxation is affected by the viscoelastic and restorative forces of the contracted myocardium (elastic recoil), myosin and actin inactivation of contraction (active relaxation), and preload reflected in the atrial pressure. The increase in ventricular stiffness in late diastole is related to titin isoforms and collagen production in myocardial interstitial tissues, and these factors also contribute to early diastolic elastic recoil and restoring force. This review explains the importance of understanding the pathophysiology and components of ventricular diastolic function using the concept of pressure phase plane and pressure-volume loop, in addition to the evaluation of diastolic function by echocardiography.

In cardiac catheterization therapy, balloon valvuloplasty and angioplasty are currently the most established treatments for congenital heart diseases in pediatric patients. Balloon pulmonary valve valvuloplasty, balloon pulmonary angioplasty, and balloon aortic valvuloplasty are common procedures in clinical practice. This review first explains the characteristics of the balloon catheter and the fundamental techniques for its use. These are essential pieces of information for the operator regardless of the lesion. Subsequently, the review presents an overview of interventional procedures for the pulmonary valve, pulmonary artery, aortic valve, and postoperative shunt stenosis. Depending on the targeted treatment site, the indications, types of balloons to be selected, appropriate balloon size, balloon inflation pressure, and balloon inflation methods vary. Thus, understanding these differences based on the targeted treatment site is crucial for effective and safe balloon valvuloplasty and angioplasty procedures.

Congenital long QT syndrome (LQTS), a genetic disorder, is characterized by delayed repolarization and a long QT interval on 12-lead electrocardiography (ECG). The hallmark of LQTS is syncope, convulsion, sudden cardiac death, and aborted cardiac arrest caused by torsade de pointes. Variations in genes encoding for cardiac ion channels, accessory ion channel subunits, or proteins modulating the function of the ion channel have been identified in 17 genes as disease-causing mutations. However, an international, evidence-based reappraisal of genes reported that LQT1, LQT2, and LQT3 are the major three types. The genetically determined prevalence of LQTS is approximately 1 : 2000. In the general population, the probability of diagnosing LQTS through ECG is 1 : 1000 in seventh graders (aged 12 years). Treatment was implemented based on the genotype–phenotype relationship. The prognosis of patients with LQTS, particularly those who are diagnosed by a school-based ECG screening program, has been improving through the control of lifestyles and well adherence to pharmacotherapy.

Cardiac resynchronization therapy (CRT) is a method of treating heart failure using a device. It is an established treatment for heart failure in adults, most commonly in patients with dilated cardiomyopathy (DCM). However, its efficacy in children with DCM has not been established. Pacemaker-induced cardiomyopathy may occur during pacemaker therapy for complete atrioventricular block in children because the ventricular lead is placed in the right ventricular free wall or outflow tract. The efficacy of CRT for pacemaker-induced cardiomyopathy in children is well established. However, the uniqueness and diversity of pediatric and congenital heart diseases make it difficult to establish guidelines for CRT; thus, CRT indications should be carefully considered in each case.

Various techniques for treating aortic valve disease have been proposed and implemented for cardiac surgery. However, existing methods have certain limitations; therefore, we are always looking for new alternatives. Choosing the best possible technique is important, particularly in children, and the balance of the risks and benefits of the various options for aortic valve surgery remains an issue. The OZAKI procedure involves reconstructing the aortic valve with three separate pieces of autologous pericardium using specialized instruments and standardized techniques to ensure the reconstruction of a reproducible aortic valve. This procedure involves the independent reconstruction of each aortic valve leaflet and aims to reproduce the natural dynamics of the valve leaflets. Notably, aortic valve disease affects children throughout their lives; thus, long-term treatment strategies must be developed. This study shows that the OZAKI procedure is worth considering an option for growing children.

The three major types of assisted circulation for severe heart failure in children are as follows: (1) extracorporeal membrane oxygenation (ECMO), (2) extracorporeal ventricular assist device, and (3) implantable ventricular assist device. Of these, ECMO is generally limited to approximately 1 month of assistance, whereas the ventricular assist device can be used for a longer term. The EXCOR^® Pediatric external ventricular assist device can be used in neonates weighing as little as 3 kg and is primarily used as a bridge to heart transplantation. In some cases, an implantable artificial heart is indicated for relatively large children, so they can be discharged from the hospital and go back to school. In Japan, very few heart transplants have been conducted for congenital heart disease, with less than 10 cases by 2022, and approximately 4% of the patients are on the waiting list. In the future, the demand for artificial hearts and transplants for congenital heart disease is expected to increase, requiring treatment strategies for these diseases.