TLDR Minoxidil may cause heart issues in animals and humans.
The study investigated the effects of minoxidil on animals and humans. Dogs treated with minoxidil developed lesions in the right atrium of the heart, while humans showed an increasing frequency of histologic changes related to age and hypertension. The study suggests that minoxidil may cause cardiac pathology in animals and humans.
102 citations,
September 1977 in “The Lancet” Minoxidil with propranolol and diuretics lowers blood pressure but causes fluid retention and hair growth.
43 citations,
January 1977 in “Toxicology and Applied Pharmacology” Minoxidil is mostly safe, but high doses can cause electrolyte imbalances and heart issues in dogs.
18 citations,
July 1975 in “Clinical Pharmacology & Therapeutics” Oral minoxidil effectively controls blood pressure quickly and safely.
180 citations,
July 1973 in “The New England Journal of Medicine” Minoxidil effectively lowers blood pressure with few side effects.
28 citations,
January 1989 in “Toxicologic Pathology” Minoxidil may cause heart changes; use caution and monitor patients with heart conditions.
27 citations,
August 1984 in “Experimental and Molecular Pathology” 
23 citations,
June 1996 in “Toxicology” Older rats more affected by minoxidil's cardiotoxic effects than younger rats.
34 citations,
January 1989 in “Toxicologic Pathology” A study found that minoxidil can damage the hearts of dogs and pigs, cautioning its use in humans.
43 citations,
January 1977 in “Toxicology and Applied Pharmacology” Minoxidil is mostly safe, but high doses can cause electrolyte imbalances and heart issues in dogs.
