Nuts have a good reputation for heart health. It is worth separating what is well established from what is still uncertain, and where cashews sit in particular.
What is reasonably well established
Large observational studies have consistently associated regular nut consumption with lower cardiovascular risk. The PREDIMED trial, which randomised participants to a Mediterranean diet supplemented with mixed nuts, found a reduction in major cardiovascular events compared with a low-fat control diet. That is stronger evidence than observation alone.
Where cashews specifically fit
Most of that research used mixed nuts, walnuts or almonds. Cashew-specific trials are fewer and smaller. Those that exist have generally found modest improvements in blood lipid measures, but the studies are short and the participant numbers small, so the honest position is that cashews are probably beneficial in line with other nuts rather than proven to be so independently.
The plausible mechanisms
Cashews are low in saturated fat relative to their total fat, and rich in monounsaturated fat. They supply magnesium, which is involved in blood pressure regulation, and contain plant sterols that modestly interfere with cholesterol absorption. None of these is dramatic on its own; together they are a reasonable explanation for a small effect.
The portion caveat
Cashews are calorie-dense, and the benefits assume they are replacing something less good rather than being added on top of an unchanged diet. Around 30g a day is the portion used in most of the research. Swapping an evening packet of fried snacks for a handful of cashews is a meaningful change; adding cashews to the fried snacks is not.
Salted versions
If you are managing blood pressure, salted cashews work against the thing you are trying to improve. Plain or roasted-unsalted are the better default for daily eating.
The sensible summary
Cashews are a reasonable part of a heart-healthy pattern of eating. They are not a treatment, they do not offset an otherwise poor diet, and they should not replace medication or medical advice. If you have diagnosed heart disease or high cholesterol, discuss dietary changes with your doctor rather than relying on general articles — this one included.