Grey's Anatomy

Denny Duquette

1969-2005

Denny Duquette, Jr.  Denny first enters the hospital in the middle of Season 2, in the episode Begin the Begin, hoping to get a heart since he is on the National Donor List. He leaves after he doesn't get it, but not before flirting with Izzie. He asks her personal questions, like if she is dating Alex Karev, a fellow intern at Seattle Grace Hospital, and when she says she is not, he gives her reasons to go out with him, instead of Alex. Denny returns to the hospital a few episodes later, causing Izzie to break up with her now boyfriend, Alex. As Denny is in the hospital, he and Izzie get much closer as each day goes on. Izzie spends the majority of her time with Denny, on and off duty.

Later on in Season 2, an opportunity arises where Denny has the chance to get a heart from another hospital, Mercy West. However, there are two claims to the heart and Dr. Preston Burke, head of cardiothoracic surgery at Seattle Grace, finds out that Denny is 17 seconds behind the other person on the donor list. In an attempt to ensure that Denny gets the heart, Izzie cuts his LVAD (Left Ventricular Assist Device) wire hoping that Denny's condition worsens to the point that Denny gets the heart, but Burke is shot on his way back to check on Denny. Denny proposes to Izzie thinking he is dying and when he does get the heart, Izzie agrees to marry Denny. However, Denny dies of a stroke shortly after Izzie accepts his proposal. Izzie does not know this at the time, but Denny is a millionaire. A few episodes later, she finds out that he left her $8.7 million. After a long debate on what to do with the money, Izzie uses it to start the Denny Duquette Memorial Clinic in honor of her fiancé. (1)

Denny appeared in season two in eleven episodes and in season 3 in two episodes.

Also, after season three ended, Jeff hosted  Grey's Anatomy: Every Moment Counts, a look back at previous episodes of the show. 

EPISODES

Season Two:

Begin the Begin

What Have I Done to Deserve This

Band-Aid Covers the Bullet Hole

Superstition

The Name of the Game

Blues for Sister Someone

Damage Case

17 Seconds

Losing My Religion

Deterioration of the Fight or Flight Response

What I Am (voice only)

Season Three:

Drowning on Dry Land

Some Kind of Miracle 

(1) Wikipedia