The primary objective of this study is to assess the effect of a therapeutic and supratherapeutic oral dose of JMKX003142 on the corrected cardiac QT interval relative to a placebo in healthy participants

Inclusion Criteria:

1. Participants must be able to return to the study center for follow-up visits as required by the protocol and be willing to comply with study policies, procedures, and constraints. They must be able to communicate effectively with the investigator, complete study-related materials, and understand the contents of the Informed Consent Form (ICF). A written ICF must be signed before any study-specific procedures are performed.
2. Healthy Chinese males or females based on medical history and physical examination. At the time of signing the informed consent form (ICF), participants must be aged 18 to 45 years (inclusive), with a body weight ≥ 50 kg and a body mass index (BMI) between 19.0 and 28.0 $kg/m^2 (inclusive).
3. Participants' health status will be determined by the investigator based on medical history, physical examination, clinical laboratory tests, and 12-lead electrocardiogram (ECG). All test results must be confirmed by the investigator as either normal or abnormal without clinical significance (NCS).
4. Participants of childbearing potential must have no plans to conceive, freeze, or donate sperm/eggs from the time of signing the informed consent form (ICF) until 3 months after the last dose, and must agree to use highly effective contraception methods.

Exclusion Criteria:

1. History or presence of clinically significant diseases, including but not limited to: cardiovascular, respiratory, gastrointestinal, hematological, genitourinary, endocrine and metabolic, neurological, psychiatric, musculoskeletal, dermatological, lymphatic, or immunological systems, or diseases of the sense organs, as well as current systemic or local acute/chronic infections.
2. Participants with any condition that increases the risk of bleeding, such as acute gastritis or active ulcers with bleeding, clinically significant thrombocytopenia or anemia, active pathological bleeding, or a history of intracranial hemorrhage.
3. Vital signs at screening that meet any of the following criteria: systolic blood pressure (SBP) ≥ 140 mmHg or < 90 mmHg; diastolic blood pressure (DBP) ≥ 90 mmHg or < 50 mmHg; pulse rate > 100 bpm or < 50 bpm; or axillary temperature > 37.2°C.
4. History of QTc interval prolongation, or any clinically significant abnormal ECG findings at screening as determined by the investigator, or QTcF ≥ 450 ms, or QRS duration > 120 ms, or PR interval ≥ 200 ms.
5. Clinical laboratory test results at screening showing serum potassium, magnesium, or calcium levels outside the normal range and judged by the investigator to be clinically significant.