Restrictive: a heart that cannot relax
In restrictive cardiomyopathy, the chamber is often a normal size and the squeeze is near-normal — yet the patient is in heart failure. The fault is diastole: the wall has become so rigid that it resists filling. Picture trying to inflate a leather balloon. Pressure has to climb very high just to admit a little blood, and that pressure backs up into the lungs and body, causing breathlessness and swelling.
Amyloidosis: a protein that infiltrates
The most important infiltrative cause of a stiff heart is cardiac amyloidosis. Here an abnormal protein folds the wrong way and deposits between the muscle cells as waxy, insoluble fibres. The wall thickens — so it can *look* like HCM on a quick scan — but this thickening is dead infiltrate, not working muscle, so the heart grows both thick and stiff and, in time, weak. It was once thought rare; better imaging and blood tests now show it is an under-recognised driver of HFpEF, especially in older adults.
Why care about naming it precisely? Because a clue-driven work-up — thick walls on echo with a paradoxically low-voltage ECG, a tell-tale pattern on cardiac MRI or a bone-tracer scan — can pin the diagnosis, and certain amyloid subtypes now have specific drugs that slow the disease. A stiff heart is no longer automatically a dead end.
Myocarditis: muscle under attack
Myocarditis is inflammation of the heart muscle, most often triggered by a viral infection — the immune response, meant to clear the virus, damages muscle in the crossfire. It can be mild and self-limited, or it can swell and weaken the heart enough to mimic acute dilated cardiomyopathy. It often strikes younger people and may follow a recent flu-like illness by days to weeks.
Because inflamed muscle leaks its contents, the blood troponin often rises — the same marker used for heart attacks — which is why myocarditis can masquerade as a heart attack in a young person with normal arteries. Cardiac MRI is the non-invasive test that best shows inflammation and oedema. Most viral myocarditis is treated supportively and a good share recovers fully; the danger is the minority that progress to chronic heart failure or throw off dangerous arrhythmias in the acute phase.