A Study to Learn More About How Well Aficamten Works in Japanese Participants With Symptomatic Obstructive Hypertrophic Cardiomyopathy

Researchers are looking for a better way to treat Japanese people who have symptomatic obstructive hypertrophic cardiomyopathy (symptomatic oHCM). Obstructive hypertrophic cardiomyopathy (oHCM) is a type of heart disease where the heart muscles become thicker than normal due to over contraction. This thickening makes it harder than normal due to over contraction. This thickening makes it harder for the heart to pump blood out to the rest of the body. In symptomatic oHCM people with the condition experience symptoms like shortness of breath, chest pain, fainting, high blood pressure and irregular heartbeats. The study treatment aficamten, also called BAY3723113, is under development to treat symptomatic oHCM. It aims to reduce the activity of cardiac myosin, a protein that helps heart muscles to contract, and thereby preventing over contraction and muscle thickening. Although treatment options are available for symptomatic oHCM, there is still need for other treatment options that help target the root cause of the condition. In this study, researchers want to understand about the effects and long-term safety of aficamten in Japanese people with symptomatic oHCM. The main purpose of the study is to learn how well aficamten works in Japanese with symptomatic oCHM. For this, the researchers will check how participant's heart blood flow changes after 6 months of treatment. They do this by measuring the pressure needed for blood to leave the heart using a test called the left ventricular outflow tract (LVOT) gradient and a special breathing technique called Valsava maneuver. Researchers will also look for: * the number of participants who will have at least 1 level improvement on a scale doctors use to assess the effect of heart problems on daily activities after 3 and 6 months of treatment * the change in the impact of heart problems on participant's daily lives based on their feedback on a questionnaire called Kansas City Cardiomyopathy Questionnaire - Clinical Summary Score (KCCQ-CSS) after 3 and 6 months of treatment. This study will have 2 treatment periods: main treatment period and long-term treatment period. During the main treatment period, participants will take aficamten tablets once daily by mouth for up to 6 months. After completing this period, the participants who can join the long-term treatment period will continue taking aficamten until the drug becomes commercially available in Japan or the study ends. Each participant will be in the study as long as they benefit from the treatment. Participants will visit the study site: * once before the treatment starts * 9 times with a gap of 2 to 4 weeks between the visits during treatment under the main treatment period, and in the long-term treatment period, participants will visit almost every 3 months until the treatment ends. * then 2 more times with a gap of 1 month between the visits after the treatment ends. During the study, the study doctors and their team will: * check participant's health by performing tests such as blood and urine tests, and checking heart health using an electrocardiogram (ECG) and echocardiogram (ECHO) * ask the participants questions about how they are feeling and what adverse events are they having An adverse event is any medical problem that a participant has during a study. Study doctors keep track of all adverse events, irrespective if they think it is related or not to the study treatment. In addition, the participants will be asked to complete a questionnaire on quality of life at certain time points during the study. If the participant benefits from the treatment, treatment with aficamten after the end of the study might be possible.