The investigators will determine the feasibility of identifying and quantifying changes in interstitial and intravascular congestion by imaging in participants with heart failure. The investigators will either continue or temporarily suspend both loop diuretics and mineralo-corticoid antagonists (MRA) for 48 hours in participants with heart failure that is both stable and mild and compare measurements of interstitial (B-lines) and intra-vascular fluids (IVC and JV diameter and renal venous flow) by ultrasound and, in a subset of participants without contra-indications, by cardiac MRI.

Inclusion Criteria:

• Clinical diagnosis of heart failure
• Plasma NT-proBNP >125ng/L or BNP >35 ng/l
• Left ventricular ejection fraction (LVEF) <50% on prior imaging test
• Treated routinely with a daily dose of loop diuretic
• Receiving other guideline-indicated therapy for heart failure
• Willing to sign the informed consent form
• Greater than 18 years of age

Exclusion Criteria:

• Chronic Kidney Disease Stage 4 or worse (eGFR <30 mL/min/1.73 m²)
• Atrial fibrillation
• Significant valve disease (investigators opinion)
• Breathlessness or chest pain at rest or minor exertion
• Patients unable to lie flat
• Patients deemed too unstable to miss treatment with diuretics for 48 hours
• Patients taking part in another interventional trial
• Any other concomitant condition that in the opinion of the investigator would not allow a safe participation in the study (ie:-pregnancy, significant frailty)
• Patients unwilling or unable to consent
• For patients willing to undergo MRI; contraindication to MRI including claustrophobia, metalworkers, and intra-orbital or intracranial metal (eg:- stents), and non-MRI compliant device.