For a patient with stable, well-controlled heart disease, first-line treatment for erectile dysfunction is usually a PDE-5 inhibitor, prescribed after a clinician reviews cardiac stability and medicines:

These drugs can generally be used in stable coronary artery disease or compensated heart failure. Current Princeton IV guidance supports their cardiovascular safety in appropriately assessed patients, as summarized by the ACC review of the guideline. Goldman-Cecil notes that PDE-5 inhibitors can be useful in compensated heart failure. - Goldman-Cecil Medicine, p. 3884

Do not use PDE-5 inhibitors if the patient takes nitrates, including nitroglycerin tablets/spray/patch, isosorbide mononitrate, or isosorbide dinitrate. The combination can cause dangerous, potentially life-threatening low blood pressure.

Important timing:

Also avoid or defer ED medication until cardiology review if there is:

If nitrates are essential, non-PDE-5 options include a vacuum erection device, alprostadil urethral or intracavernosal therapy, and in selected cases a penile prosthesis. Intracavernosal alprostadil is a recognized second-line therapy. - Goldman-Cecil Medicine, Erectile Dysfunction section

Because the correct choice depends on the exact cardiac diagnosis and drugs, the patient should have the medication list reviewed by their cardiologist or prescribing doctor before starting treatment.