Blood tests can check for:
Anemia, cholesterol level, blood sugar level, kidney, liver and thyroid function
B-type natriuretic peptide (BNP)* - produced at a higher rate by failing heart muscle
(* BNP has recently emerged as a potentially important clinical marker in HF. It helps in cases with unexplained dyspnea in both ambulatory and hospital settings.  )
Exercise stress tests can be performed to determine how the heart functions under load. This can reveal information on:
The ECG performed during the exercise stress test cannot diagnose heart failure directly, but it can detect other cardiac conditions which are often precursors to heart failure such as coronary artery disease or arrhythmias.
X-Ray - can show enlarged heart and pulmonary congestion