"This is just my theory but clen as well as ephedrine binds to beta-1-agonist receptor which are located in the heart."
Clen is considered a selective beta-2 agonist, but very few are totally selective, therefore clen can and will cross-react with the beta-1 subtype. Ephedrine, on the other hand, is non-selective, thus binding all 3 subtypes.
"Clen is more powerful than ephedrine so I think it would do more damage short term, but ephedrine is used for longer periods of time, so I would be more concerned with ephedrine use."
Clen is a stronger drug, mg/mg, compared to ephedrine, but because it is more selective for the beta-2 receptor, it is less cardio-toxic than ephedrine.
We can't yet jump to conclusions concerning cardiac hypertrophy, which many assume to be dangerous. Cardiac hypertrophy occurs with exercise and is considered beneficial. Some researchers have considered using beta-1 agonists for increasing heart strength for certain patients who are undergoing heart surgery.
Cardiac enlargement that IS considered dangerous tends to be associated with fibrosis of the heart, where sections of the heart tissue die and is replaced with scar tissue (fibrotic tissue), often due to blockage of vessels that supply blood to the cardiac tissue. Fibrous tissue has no elasticity and contractility, and is therefore non-functional.
Before anyone thinks that I am advocating large intakes of cardiac stimulants, let me clarify: I don't believe the use of large quantities of steroids, T-3, adrenergics, GH and insulin is beneficial to the heart, but I don't think that moderate use of one or more of these agents is deadly.