Unstable angina pectoris is nowadays defined as an acute coronary syndrome commonly marked by a non-specific electrocardiogram changes.
[facta.junis.ni.ac.rs]
Heart attack: Non-ST segment elevation myocardial infarction (NSTEMI) This heart attack, or MI, may not cause changes on an electrocardiogram (ECG).
[my.clevelandclinic.org]
[…] in your electrocardiogram, frequent and/or repeated angina or chest pain in the past # days, heart failure, severe heart rhythm disorders, right-to-left shunts of the heart
[mt.glosbe.com]