Coronary Artery Disease (CAD): This is the most common cause of a failed stress test, as it directly affects the heart's ability to respond to increased demand during exercise or pharmacological stress. CAD can lead to ischemia, which is often detected by stress tests.

Cardiomyopathy: Conditions such as hypertrophic cardiomyopathy can lead to abnormal stress test results due to impaired heart function and potential for ischemia.
Valvular Heart Disease: Significant valvular disease, such as aortic stenosis or mitral regurgitation, can cause a failed stress test due to the heart's inability to adequately increase cardiac output in response to stress.
Hypertension: Uncontrolled hypertension can lead to left ventricular hypertrophy and increased risk of CAD, contributing to a failed stress test.

Acute Coronary Syndrome (ACS): Although less common, a failed stress test could be an indicator of an impending or ongoing ACS, including myocardial infarction. Missing this diagnosis could be catastrophic.
Cardiac Arrhythmias: Certain arrhythmias, especially those that impair cardiac function, such as atrial fibrillation with rapid ventricular response or ventricular tachycardia, can cause a failed stress test and require immediate attention.
Pulmonary Embolism: Though less directly related to stress test failure, significant pulmonary embolism can lead to cardiac strain and failure, mimicking a cardiac cause for a failed stress test.

Cardiac Sarcoidosis: A rare condition where granulomatous inflammation affects the heart, potentially leading to conduction abnormalities, arrhythmias, and heart failure, which could result in a failed stress test.
Amyloidosis: Involvement of the heart by amyloid deposits can lead to restrictive cardiomyopathy, which might cause abnormal results on a stress test.
Arteritis (e.g., Takayasu Arteritis): Inflammation of the arteries can lead to stenosis or occlusion, affecting blood flow and potentially causing a failed stress test, especially if the coronary arteries are involved.